volser: Remove ExtractVolId

volser: Remove ExtractVolId

volser was using its own function to extract a volume ID from a
filename string, and was using atol to do so. The ato* family of
functions can have problems with larger volume IDs, not to mention a
lack of error checking, so don't use it. Since we already have the
function VolumeNumber in the vol package to do the very same thing,
just use that instead.

Reviewed-on: http://gerrit.openafs.org/5594
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 87f969f82d12c8200ede3fd30a151e09ab0bf6ad)

Change-Id: I4f047c4141493e151db0a6b5ec21bee3af35e040
Reviewed-on: http://gerrit.openafs.org/5720
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>