Bug 1323951 - Don't show the compact tabs setting on tablets. r=sebastian

preferences_general_tablet.xml actually only applies on tablets with enough room
for multiple panes, otherwise preferences_general.xml is used; so the fix here
is necessary to remove the pref on tablets not large enough for multiple
preferences panes.

MozReview-Commit-ID: Ff7VebVYV10

--HG--
extra : rebase_source : fda5012f3edd371de5c431e6c50258de4017f547

mobile/android/base/java/org/mozilla/gecko/preferences/GeckoPreferences.java

@@ -884,6 +884,10 @@ public class GeckoPreferences
                     preferences.removePreference(pref);
                     i--;
                     continue;
+                } else if (PREFS_COMPACT_TABS.equals(key) && HardwareUtils.isTablet()) {
+                    preferences.removePreference(pref);
+                    i--;
+                    continue;
                 }
 
                 // Some Preference UI elements are not actually preferences,