Move removeUserWithProfilesUnchecked outside of mPackagesLock.

In UserManagerService.removeUserWhenPossible we're first trying to
remove the user immediately by calling removeUserWithProfilesUnchecked
or otherwise marking it as ephemeral. In that flow if the user's type
is a profile, we're calling sendProfileRemovedBroadcast inside
removeUserUnchecked method. Which requires an ActivityManager lock and
shouldn't be called while holding PackageManager lock, or it might
cause a deadlock.

This CL moves that call outside of mPackagesLock to prevent such a
deadlock possibility.

And also deduplicates the user removal validation logic into
getUserRemovabilityLocked.

Bug: 269077555
Test: atest com.android.server.pm.UserManagerTest
Change-Id: I46a1675fe181892eac3fba6625ff49adb60441bb