Allow profiles on any full user.

Profiles used to be restricted just to the SYSTEM_USER (and later to
the main user), but from the framework point of view there is no need
for such restriction, hence this CL lifts it.

Test: atest FrameworksCoreTests:UserInfoTest
Test: adb shell aflags enable android.multiuser.profiles_for_all && adb reboot && adb shell pm create-user Homer && adb shell pm create-user --profileOf 11 --managed Bart
Bug: 374832167
Flag: android.multiuser.profiles_for_all

Change-Id: I5b4f89e24bb67656ccbd4447fee40f5078d39024