procfs.c: Don't install a deprecated_xfer_memory method

This removes yet another instance of a deprecated_xfer_memory user,
and fixes a nasty regression as a side-effect:

    (gdb) start
    Temporary breakpoint 1 at 0x19070: file simple_main.adb, line 4.
    Starting program: /[...]/simple_main
    Warning:
    Cannot insert breakpoint 1.
    Cannot access memory at address 0x19070
    Cannot insert breakpoint -3.
    Temporarily disabling shared library breakpoints:
    breakpoint #-3

The regression was introduced by the to_xfer_partial transition
to return a status enum.  procfs_xfer_partial was updated but
not the case where object is TARGET_OBJECT_MEMORY.  As result,
procfs_xfer_partial was returning the length xfered rather than
the status, and the xfered buffer was left uninitialized.

gdb/
2014-02-19  Pedro Alves  <palves@redhat.com>

	* procfs.c (procfs_target): Don't install procfs_xfer_memory as
	deprecated_xfer_memory hook.
	(procfs_xfer_partial): Call procfs_xfer_memory instead
	of the deprecated_xfer_memory target hook.
	(procfs_xfer_memory): Adjust interface as a to_xfer_partial
	helper.