receive-pack: switch global variable 'commands' to a parameter

receive-pack: switch global variable 'commands' to a parameter

Receive-pack is inconsistent in its usage of the 'commands'
variable; though it is setup as a global and accessed that way by
execute_commands(), report(), and run_receive_hook(), it is also
passed as a parameter to delete_only() and run_update_post_hook().

For consistency, make it local to cmd_receive_pack and pass it as a
parameter. As long as we're cleaning up, also make our use of the
names 'commands' and 'cmd' consistent.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>