Gallery : Remove DialogPicker theme in v21

Crashes widget selection :

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
 	at com.android.internal.app.WindowDecorActionBar.getDecorToolbar(WindowDecorActionBar.java:238)
 	at com.android.internal.app.WindowDecorActionBar.init(WindowDecorActionBar.java:191)
 	at com.android.internal.app.WindowDecorActionBar.<init>(WindowDecorActionBar.java:165)
 	at android.app.Activity.initWindowDecorActionBar(Activity.java:2127)
 	at android.app.Activity.setContentView(Activity.java:2145)
 	at com.android.gallery3d.app.AbstractGalleryActivity.setContentView(AbstractGalleryActivity.java:142)
 	at com.android.gallery3d.app.PickerActivity.onCreate(PickerActivity.java:48)
 	at com.android.gallery3d.app.DialogPicker.onCreate(DialogPicker.java:28)
 	at android.app.Activity.performCreate(Activity.java:5933)
	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)

Change-Id: I9d83526153794e8bc0cc6ec46735ff883f004e60
(cherry picked from commit 5a5691a9966be2e39bc3c45a2e48d8e22f69a292)