Fix PR remote/9053: remove dead code on query packet size

Fix PR remote/9053: remove dead code on query packet size

The code becomes dead as GDB evolves.  In 2003, Andrew Cagney post patch
https://sourceware.org/ml/gdb-patches/2003-10/msg00511.html to add target
read/write partial methods.  They support query buffer size when both
OFFSET and LEN is zero, and it was used in avr-tdep.c and kod.c.  Then,
Daniel added target_read_object_alloc and avr-tdep.c switches to use that
in patch https://sourceware.org/ml/gdb-patches/2006-07/msg00009.html
From then on, GDB on longer queries the buffer size, so the code
returning packet size in remote_xfer_partial became dead.

PR 17060 is duplicated of PR 9053, so I mention the latter in the
ChangeLog entry.  Rebuild GDB with this patch.  OK to apply?
I'll mark PR 17060 as duplicated once the patch is applied.

gdb:

2014-08-09  Yao Qi  <yao@codesourcery.com>

	PR remote/9053
	* remote.c (remote_xfer_partial): Remove dead code.