apply: remove unused call to free() in gitdiff_{old,new}name()

apply: remove unused call to free() in gitdiff_{old,new}name()

These two functions keep a copy of filename it was given, let
gitdiff_verify_name() to rewrite it to a new filename and then free
the original if they receive a newly minted filename.

However

 (1) when the original name is NULL, gitdiff_verify_name() returns
     either NULL or a newly minted value.  Either case, we do not
     have to worry about calling free() on the original NULL.

 (2) when the original name is not NULL, gitdiff_verify_name()
     either returns that as-is, or calls die() when it finds
     inconsistency in the patch.  When the function returns, we know
     that "if ()" statement always is false.

Noticed by Christian Couder.

Signed-off-by: Junio C Hamano <gitster@pobox.com>