UserManagerService: clear calling identity in getCredentialOwnerProfile()

Add the missing Binder.clearCallingIdentity() to
UserManagerService#getCredentialOwnerProfile(), just after the
checkManageUsersPermission().  This avoids a warning in
UserManager#getUserProperties() about the system fetching UserProperties
on behalf of another uid.  Since checkManageUsersPermission() ensures
that the caller can see all the user properties anyway, the actual
result should remain the same (besides the warning message going away).

Bug: 403355811
Test: atest FrameworksServicesTests:UserManagerServiceTest
Flag: EXEMPT bugfix
Change-Id: I635a15afef5fa9d0b1b04c5a203e19a6df30fdb7