Merge "Removing non SYSTEM user before running systemUserOnlyTest" into main

    @Test

    public void testGetBootUser_Headless_ThrowsIfOnlySystemUserExists() throws Exception {

        setSystemUserHeadless(true);

        removeNonSystemUsers();

        assertThrows(UserManager.CheckedUserOperationException.class,

                () -> mUmi.getBootUser(/* waitUntilSet= */ false));

    }

    private void removeNonSystemUsers() {

        for (UserInfo user : mUms.getUsers(true)) {

            if (!user.getUserHandle().isSystem()) {

                mUms.removeUserInfo(user.id);

            }

        }

    }

    private void mockCurrentUser(@UserIdInt int userId) {

        mockGetLocalService(ActivityManagerInternal.class, mActivityManagerInternal);