Removing non SYSTEM user before running systemUserOnlyTest

Bug: 295446676
Test: atest UserManagerServiceTest -c
Change-Id: I6f536b7f5b85e4e884bd284b1848e43ac3c9029d
diff --git a/services/tests/mockingservicestests/src/com/android/server/pm/UserManagerServiceTest.java b/services/tests/mockingservicestests/src/com/android/server/pm/UserManagerServiceTest.java
index d32b6be..78e5a42 100644
--- a/services/tests/mockingservicestests/src/com/android/server/pm/UserManagerServiceTest.java
+++ b/services/tests/mockingservicestests/src/com/android/server/pm/UserManagerServiceTest.java
@@ -331,6 +331,7 @@
     @Test
     public void testGetBootUser_Headless_ThrowsIfOnlySystemUserExists() throws Exception {
         setSystemUserHeadless(true);
+        removeNonSystemUsers();
 
         assertThrows(UserManager.CheckedUserOperationException.class,
                 () -> mUmi.getBootUser(/* waitUntilSet= */ false));
@@ -504,6 +505,14 @@
                 .isFalse();
     }
 
+    private void removeNonSystemUsers() {
+        for (UserInfo user : mUms.getUsers(true)) {
+            if (!user.getUserHandle().isSystem()) {
+                mUms.removeUserInfo(user.id);
+            }
+        }
+    }
+
     private void resetUserSwitcherEnabled() {
         mUms.putUserInfo(new UserInfo(USER_ID, "Test User", 0));
         mUms.setUserRestriction(DISALLOW_USER_SWITCH, false, USER_ID);