https://github.com/kubernetes/kubernetes/pull/69782 introduced a change
to register the device attachment (in the StorageOS API) prior to the
volume attachment.  The volume attachment code would clear any mount
info, causing the StorageOS API to register the mount and then
immediately de-register it.

The code to clear the mount info on volume attach is no longer needed.
It was used to force-mount a volume if StorageOS thought it was already
mounted.  In practice it was not needed, and administrators have other
ways of clearing stale mount information if required.