Documentation/kernel-parameters: remove inttest parameter

According to grep I see no users:
| #git grep inttest
| Documentation/kernel-parameters.txt:    inttest=        [IA-64]

The parameters itself has no description what it supposed to do.
According to the history tree, it was introduced in "[PATCH] Updated
Documentation/kernel-parameters.txt" ("10414c6ddb"). By that time that
parameter had an user. It was removed later by "[PATCH] ia64: SGI SN
update" ("c6bacd5010ec") by Jesse Barnes himself.

Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Tony Luck <tony.luck@intel.com>