Remove deprecated files from integrated KTN meta layers

With the layers in a single repo, we don't need layer-specific CI configs,
READMEs or license information anymore.

layers/meta-ktn-imx/.gitlab-ci.yml

-include:
-  - project: 'sw/yocto/yocto-ktn'
-    ref: 6cd89b4db8772b695d1aad136b50812bbe98d7f1
-    file: '/ci/yocto-ktn-meta.yml'
-
-build:
-  extends: .meta-build-trigger
-  trigger:
-    project: sw/yocto/build-ktn-imx
-    branch: develop-dunfell
-
-stages:
-  - build

layers/meta-ktn-stm32mp/.gitlab-ci.yml

-include:
-  - project: 'sw/yocto/yocto-ktn'
-    ref: b7a501352cc35983033e92c9bd5361016a5f23ca
-    file: '/ci/yocto-ktn-meta.yml'
-
-build:
-  extends: .meta-build-trigger
-  trigger:
-    project: sw/yocto/build-stm32mp
-    branch: develop-dunfell
-
-stages:
-  - build

layers/meta-ktn-stm32mp/LICENSE

-All metadata in this OpenEmbedded/Yocto layer is MIT licensed (see
-LICENSE.MIT) unless otherwise stated. Source code included in tree
-for individual recipes (e.g. patches) are under the LICENSE stated
-in the associated recipe (.bb file) unless otherwise stated.
-
-License information for any other files is either explicitly stated 
-or defaults to MIT.

layers/meta-ktn-stm32mp/LICENSE.MIT

-MIT License
-
-Copyright (c) 2022 Kontron Electronics GmbH
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in 
-all copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
-THE SOFTWARE.

layers/meta-ktn-stm32mp/README.md

-# Yocto/OE meta layer for Kontron Electronics Yocto BSPs
-
-This layer provides support for Kontron Electronics BSPs, containing custom
-recipes, classes, configuration, etc.
-
-Please see https://docs.kontron-electronics.de for further information.

layers/meta-ktn/.gitlab-ci.yml

-include:
-  - project: 'sw/yocto/yocto-ktn'
-    ref: 24cb378341b3db63d64abb69c95b5b90ea5f6f98
-    file: '/ci/yocto-ktn-meta.yml'
-
-build-imx:
-  extends: .meta-build-trigger
-  trigger:
-    project: sw/yocto/build-ktn-imx
-    branch: develop-dunfell
-
-build-mp1:
-  extends: .meta-build-trigger
-  trigger:
-    project: sw/yocto/build-stm32mp
-    branch: develop-dunfell
-
-stages:
-  - build

layers/meta-ktn/LICENSE

-All metadata in this OpenEmbedded/Yocto layer is MIT licensed (see
-LICENSE.MIT) unless otherwise stated. Source code included in tree
-for individual recipes (e.g. patches) are under the LICENSE stated
-in the associated recipe (.bb file) unless otherwise stated.
-
-License information for any other files is either explicitly stated 
-or defaults to MIT.

layers/meta-ktn/LICENSE.MIT

-MIT License
-
-Copyright (c) 2022 Kontron Electronics GmbH
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in 
-all copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
-THE SOFTWARE.

layers/meta-ktn/README.md

-# Yocto/OE meta layer for Kontron Electronics Yocto BSPs
-
-This layer provides support for Kontron Electronics BSPs, containing custom
-recipes, classes, configuration, etc.
-
-Please see https://docs.kontron-electronics.de for further information.