Merge pull request #7024 from Stypox/string-fixes

Never use ``android.R.string``s; remove unused ``add`` string

app/src/main/java/us/shandian/giga/ui/adapter/MissionAdapter.java

@@ -555,7 +555,7 @@ public class MissionAdapter extends Adapter<ViewHolder> implements Handler.Callb
             );
         }
 
-        builder.setNegativeButton(R.string.finish, (dialog, which) -> dialog.cancel())
+        builder.setNegativeButton(R.string.ok, (dialog, which) -> dialog.cancel())
                 .setTitle(mission.storage.getName())
                 .create()
                 .show();