remove unused strings and colors

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

app/src/main/res/values/colors.xml

@@ -63,7 +63,6 @@
     <color name="nc_darkGreen">#006400</color>
     <color name="controller_chat_separator">#E8E8E8</color>
     <color name="grey_600">#757575</color>
-    <color name="grey_900">#212121</color>
     <color name="nc_grey">#D5D5D5</color>
     <color name="controller_call_incomingCallTextView">#E9FFFFFF</color>
     <color name="grey950">#111111</color>

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

@@ -681,9 +681,7 @@ How to translate with transifex:
     <string name="translation_error_message">Could not detect language</string>
     <string name="translation_copy_translated_text">Copy translated text</string>
     <string name="nc_filter">Filter Conversations</string>
-    <string name="nc_filter_short">Filter</string>
     <string name="mentioned">Mentioned</string>
     <string name="unread">Unread</string>
-    <string name="no_filter">No Filter</string>
 
 </resources>