Clear the format metadata cache for a book when a format is deleted.

src/calibre/library/database2.py

@@ -1333,6 +1333,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
     def remove_format(self, index, format, index_is_id=False, notify=True,
                       commit=True, db_only=False):
         id = index if index_is_id else self.id(index)
+        del self.format_metadata_cache[id]
         name = self.conn.get('SELECT name FROM data WHERE book=? AND format=?', (id, format), all=False)
         if name:
             if not db_only: