Revert "regulator: pca9450: Add SD_VSEL GPIO for LDO5"

This reverts commit 8c67a11b.

It turns out that all boards using the PCA9450 actually have the
SD_VSEL input connected to the VSELECT signal of the SoCs SD/MMC
interface. Therefore we don't need manual control for this signal
via GPIO and threre aren't any users.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
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Changes for v2:
* rebase to current master