Remove old strings

Remove strings which have been deleted from the English strings file during development, but were translated via Weblate, which failed to pull and push our upstream repo.

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

@@ -156,8 +156,6 @@
     <string name="audio">Аудио</string>
     <string name="retry">Опитай отново</string>
     <string name="storage_permission_denied">Достъпа до хранилището е отказан</string>
-    <string name="use_old_player_title">Използвай стария плейър</string>
-    <string name="use_old_player_summary">Използваю стария вграден Mediaframewoek плейър</string>
 
     <plurals name="subscribers">
 	<item quantity="one">%s абонат</item>