Cleanup RespondViaSmsSettings class.

Remove inner class, so there is just one class which extends
PreferenceActivity.

Bug: 19372734
Change-Id: I0cd1095edf12261b5957c9474238bcaaf3005831
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index ef04eb0..4fc2542 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -193,7 +193,7 @@
             </intent-filter>
         </receiver>
 
-        <activity android:name=".RespondViaSmsSettings$Settings"
+        <activity android:name=".RespondViaSmsSettings"
                   android:label="@string/respond_via_sms_setting_title"
                   android:configChanges="orientation|screenSize|keyboardHidden"
                   android:theme="@style/Theme.Telecom.DialerSettings"