Rename the script to refer to phabricator, not toby.

The extra disk on the toby machine only holds phabricator data.  This
is unlikely to change -- phabricator deserves its own disk, we'd be
more likely to add a second disk if need be.  So update this script to
make it clear it's phabricator data that's being backed up here.

(I care because I'm moving phabricator off toby sometime soon, and
don't want to keep the -- now misleading -- toby name when that
happens.)

Auditors: alpert

Test Plan:
Fingers crossed.  Will check tomorrow to make sure the nightly backup
to s3 still happened.