Prepare tests for impending robolectric merge

Setting's ShadowUserManager.reset() was unnecessary and collided with a
newly introduced reset() method in its super class. It has been removed.

Test: make -j56 RunSettingsGoogleRoboTests &&
  make -j56 RunSettingsRoboTests &&
  make -j56 RunSettingsLibRoboTests

Change-Id: I63c50eca0de3581fd4f64f4862233446f5937d0c

tests/robotests/src/com/android/settings/security/RestrictedEncryptionPreferenceControllerTest.java

@@ -63,11 +63,6 @@ public class RestrictedEncryptionPreferenceControllerTest {
         mUserManager = ShadowUserManager.getShadow();
     }
 
-    @After
-    public void tearDown() {
-        mUserManager.reset();
-    }
-
     @Test
     public void isAvailable_noRestriction_shouldReturnTrue() {
         assertThat(mCredentialStoragePreferenceController.isAvailable()).isTrue();