remove unused strings

src/main/res/values/strings.xml

@@ -701,12 +701,10 @@
     <string name="synced_icon">Synced</string>
     <string name="available_offline_icon">Available offline</string>
     <string name="checkbox">Checkbox</string>
-    <string name="thumbnail">Thumbnail</string>
     <string name="shared_icon_share">share</string>
     <string name="shared_icon_shared_via_link">shared via link</string>
     <string name="shared_icon_shared">shared</string>
     <string name="overflow_menu">Overflow menu</string>
-    <string name="share_file_icon">Share file icon</string>
     <string name="sort_by_name_ascending">A - Z</string>
     <string name="sort_by_modification_date_ascending">Newest first</string>
     <string name="sort_by_size_descending">Biggest first</string>