Remove unused flush from read_subunit()

The read_subunit module isn't writing anything so there isn't any
buffered data to flush. So, this commit just removes the flush() call.

Change-Id: I7c436b5c21ea11846eb0be8a608feecce37e82cf

subunit2sql/read_subunit.py

@@ -95,7 +95,6 @@ class ReadSubunit(object):
             'metadata': metadata,
             'attachments': attachment_dict
         }
-        self.stream_file.flush()
 
     def get_attrs(self, name):
         matches = self.attr_regex.search(name)