Bug 1132751 - Remove redundant ActionBar home setting. r=liuche

This is defined in the Activity theme too.

--HG--
extra : rebase_source : f97731dbef34f20338251791353a3facdccb2bd2

mobile/android/base/preferences/GeckoPreferences.java

@@ -401,13 +401,6 @@ OnSharedPreferenceChangeListener
             }
         });
 
-        if (Versions.feature14Plus) {
-            final ActionBar actionBar = getActionBar();
-            if (actionBar != null) {
-                actionBar.setHomeButtonEnabled(true);
-            }
-        }
-
         // N.B., if we ever need to redisplay the locale selection UI without
         // just finishing and recreating the activity, right here we'll need to
         // capture EXTRA_SHOW_FRAGMENT_TITLE from the intent and store the title ID.