Windows: remove unnecessary prototype from smb.c

Windows: remove unnecessary prototype from smb.c

Remove rx_StartClientThread() prototype.

Reviewed-on: http://gerrit.openafs.org/3021
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 5880a576273c3b5f7683937df42bacf506007ba2)
Change-Id: I0b61600b48239fbd30d8e8a13cc73fe33e4fe5df
Reviewed-on: http://gerrit.openafs.org/3120
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>