sys: Flag rmt_Quit as AFS_NORETURN

Help out the static analyzer by telling it that rmt_Quit never returns

Change-Id: I5ee0d2ea444706e68af5a1298fd638e7d0d7f41d
Reviewed-on: http://gerrit.openafs.org/9184
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>