Remove gdb_bfd_stash_filename to fix crash with fix of binutils/11983

Remove gdb_bfd_stash_filename to fix crash with fix of binutils/11983
https://sourceware.org/ml/gdb-patches/2014-01/msg00029.html
https://sourceware.org/ml/gdb-patches/2014-01/msg00053.html

2014-01-07  Hui Zhu  <hui@codesourcery.com>

	* gdb_bfd.c (gdb_bfd_stash_filename): Removed.
	(gdb_bfd_open): Removed gdb_bfd_stash_filename.
	(gdb_bfd_fopen): Ditto.
	(gdb_bfd_openr): Ditto.
	(gdb_bfd_openw): Ditto.
	(gdb_bfd_openr_iovec): Ditto.
	(gdb_bfd_fdopenr): Ditto.
	* gdb_bfd.h (gdb_bfd_stash_filename): Removed.
	* solib-aix.c (solib_aix_bfd_open): Alloc object_bfd->filename
	with xstrdup.
	* solib-darwin.c (darwin_bfd_open): Alloc res->filename
	with xstrdup.
	* symfile-mem.c (symbol_file_add_from_memory): Removed
	gdb_bfd_stash_filename.