process_{tree,blob}: Remove useless xstrdup calls

process_{tree,blob}: Remove useless xstrdup calls

The name of the processed object was duplicated for passing it to
add_object(), but that already calls path_name, which allocates a new
string anyway. So the memory allocated by the xstrdup calls just went
nowhere, leaking memory.

This reduces the RSS usage for a "rev-list --all --objects" by about 10% on
the gentoo repo (fully packed) as well as linux-2.6.git:

    gentoo:
                    | old           | new
    ----------------|-------------------------------
    RSS             |       1537284 |       1388408
    VSZ             |       1816852 |       1667952
    time elapsed    |       1:49.62 |       1:48.99
    min. page faults|        417178 |        379919

    linux-2.6.git:
                    | old           | new
    ----------------|-------------------------------
    RSS             |        324452 |        292996
    VSZ             |        491792 |        460376
    time elapsed    |       0:14.53 |       0:14.28
    min. page faults|         89360 |         81613

Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>