Remove SMB Provider functionality

Remove most of the guts except parts which are still used directly,
not just through the ProvidedFileSystemInterface API.

This leaves share discovery etc. in place.

Bug: 1203884
Change-Id: Icc256c020ff752123cb3011aaf32ebd9468e82f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3026308


Reviewed-by: Anand K Mistry <amistry@chromium.org>
Reviewed-by: Josh Simmons <simmonsjosh@google.com>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#902210}