Remove broken/unused Connection.getChunkFIFO method.

This method appears to be broken -- since it never removes
anything from messages, and it adds new messages to it,
the while loop is an infinite loop.  The method also does not appear
to have ever been used since the code was added in 2012, so
this commit removes it.

cc @mateiz who originally added this method in case there's a reason it should be here! (https://github.com/apache/spark/commit/63051dd2bcc4bf09d413ff7cf89a37967edc33ba)