Don't check for changeid permissions in system server

Remove compat checks for LOG_COMPAT_CHANGE, READ_COMPAT_CHANGE_CONFIG
and OVERRIDE_COMPAT_CHANGE_CONFIG in PlatformCompat when the caller
is the system server itself.

Bug: 150674197
Test: boots without spammy messages
Change-Id: I16f9d5286eff950f68cf5b2c1101ccb987fc7afe