http.c: Remove bad free of static block

http.c: Remove bad free of static block

The filename variable here is pointing to a block of memory that
was allocated by sha1_file.c and is also held in a static variable
scoped within the sha1_pack_name() function.  Doing a free() here is
returning that memory to the allocator while we might still try to
reuse it on a subsequent sha1_pack_name() invocation.  That's not
acceptable, so don't free it.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>