DelChannelUser call and semantic fixups

DelChannelUser call and semantic fixups

src/hash.c (DelChannel): Fix type of 'reason' arg to DelChannelUser().
  (DelChannelUser): Only send part message if user is local.

src/proto-bahamut.c (DelUser): Unswap arguments to DelChannelUser().
  (cmd_part): Move to proto-common.c.

src/proto-common.c (part_desc): New structure type.
  (part_helper): Use it to capture user and reason.
  (cmd_part): New common function.

src/proto-p10.c (cmd_part): Move to proto-common.c.
  (DelUser): Unswap arguments to DelChannelUser().
git-archimport-id: srvx@srvx.net--2006/srvx--devo--1.3--patch-29