http.c: Tiny refactoring of finish_http_pack_request

http.c: Tiny refactoring of finish_http_pack_request

Always remove the struct packed_git from the active list, even
if the rename of the temporary file fails.

While we are here, simplify the code a bit by using a common
local variable name ("p") to hold the relevant packed_git.

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