Remove some unused overlay code

This patch removes some unneeded initializations in overlay code in
symfile.c.  It also deletes some old commented-out code.

2016-07-14  Tom Tromey  <tom@tromey.com>

	* symfile.c (simple_overlay_update_1): Remove initialization
	of "size", and commented-out code.
	(simple_overlay_update): Likewise.