Settings: remove unuseful initialization

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/SettingsActivity.java

@@ -210,9 +210,6 @@ public class SettingsActivity extends AppCompatPreferenceActivity {
                             return false;
                         }
                     });
-
-            initializePassphraseCacheSubs(
-                    (SwitchPreference) findPreference(Constants.Pref.PASSPHRASE_CACHE_SUBS));
         }
     }
 
@@ -590,15 +587,4 @@ public class SettingsActivity extends AppCompatPreferenceActivity {
                 || ExperimentalPrefsFragment.class.getName().equals(fragmentName)
                 || super.isValidFragment(fragmentName);
     }
-
-    private static void initializePassphraseCacheSubs(final SwitchPreference mPassphraseCacheSubs) {
-        mPassphraseCacheSubs.setChecked(sPreferences.getPassphraseCacheSubs());
-        mPassphraseCacheSubs.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
-            public boolean onPreferenceChange(Preference preference, Object newValue) {
-                mPassphraseCacheSubs.setChecked((Boolean) newValue);
-                sPreferences.setPassphraseCacheSubs((Boolean) newValue);
-                return false;
-            }
-        });
-    }
 }

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/Preferences.java

@@ -107,12 +107,6 @@ public class Preferences {
         return mSharedPreferences.getBoolean(Pref.PASSPHRASE_CACHE_SUBS, false);
     }
 
-    public void setPassphraseCacheSubs(boolean value) {
-        SharedPreferences.Editor editor = mSharedPreferences.edit();
-        editor.putBoolean(Pref.PASSPHRASE_CACHE_SUBS, value);
-        editor.commit();
-    }
-
     public boolean getCachedConsolidate() {
         return mSharedPreferences.getBoolean(Pref.CACHED_CONSOLIDATE, false);
     }

OpenKeychain/src/main/res/xml/passphrase_preferences.xml

@@ -4,6 +4,7 @@
         android:key="passphraseCacheTtls"
         android:title="@string/label_passphrase_cache_ttl" />
     <SwitchPreference
+        android:defaultValue="false"
         android:key="passphraseCacheSubs"
         android:title="@string/label_passphrase_cache_subs" />
     <SwitchPreference