Remove support for v3 sig generation

OpenKeychain/src/main/res/values/strings.xml

@@ -103,7 +103,6 @@
     <string name="label_passphrase_cache_ttl">Passphrase Cache</string>
     <string name="label_message_compression">Message Compression</string>
     <string name="label_file_compression">File Compression</string>
-    <string name="label_force_v3_signature">Force old OpenPGPv3 Signatures</string>
     <string name="label_keyservers">Keyservers</string>
     <string name="label_key_id">Key ID</string>
     <string name="label_creation">Creation</string>

OpenKeychain/src/main/res/xml/adv_preferences.xml

@@ -16,7 +16,7 @@
 -->
 
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
-    <PreferenceCategory android:title="@string/section_defaults" >
+    <PreferenceCategory android:title="@string/section_defaults">
         <org.sufficientlysecure.keychain.ui.widget.IntegerListPreference
             android:key="defaultEncryptionAlgorithm"
             android:persistent="false"
@@ -33,22 +33,16 @@
             android:key="defaultFileCompression"
             android:persistent="false"
             android:title="@string/label_file_compression" />
-
         <CheckBoxPreference
             android:key="defaultAsciiArmor"
             android:persistent="false"
             android:title="@string/label_ascii_armor" />
-
+    </PreferenceCategory>
+    <PreferenceCategory android:title="@string/section_advanced">
         <CheckBoxPreference
             android:key="writeVersionHeader"
             android:persistent="false"
             android:title="@string/label_write_version_header"
             android:summary="@string/label_write_version_header_summary" />
     </PreferenceCategory>
-    <PreferenceCategory android:title="@string/section_advanced" >
-        <CheckBoxPreference
-            android:key="forceV3Signatures"
-            android:persistent="false"
-            android:title="@string/label_force_v3_signature"/>
-    </PreferenceCategory>
 </PreferenceScreen>