bsd-uthread.c: Don't install a to_xfer_partial method.

Whatever the comment about deprecated_xfer_memory refered to,
deprecated_xfer_memory is gone now.  There's no need to install a
target method that just delegates, as that's what the default
delagator does already.

Tested by building an --enable-targets=all gdb on x86_64 Fedora 17.

gdb/
2014-01-15  Pedro Alves  <palves@redhat.com>

	* bsd-uthread.c (bsd_uthread_xfer_partial): Delete function.
	(bsd_uthread_target): Don't install bsd_uthread_xfer_partial as
	to_xfer_partial method.