Use default launcher from RoleManager as the only source of truth in ShortcutManager

Bug: 159814579
Test: atest com.android.server.pm.ShortcutManagerTest1
            com.android.server.pm.ShortcutManagerTest2
            com.android.server.pm.ShortcutManagerTest3
            com.android.server.pm.ShortcutManagerTest4
            com.android.server.pm.ShortcutManagerTest5
            com.android.server.pm.ShortcutManagerTest6
            com.android.server.pm.ShortcutManagerTest7
            com.android.server.pm.ShortcutManagerTest8
            com.android.server.pm.ShortcutManagerTest9
            com.android.server.pm.ShortcutManagerTest10
            com.android.server.pm.ShortcutManagerTest11
      atest CtsShortcutHostTestCases
      atest CtsShortcutManagerTestCases

Change-Id: I93d1a3f1f45301de5307bde8dacb0000bd42147c