Rename XHPAST database

Summary: Rename the XHPAST database from {$NAMESPACE}_xpastview to {$NAMESPACE}_xhpast.

Test Plan: Ran ./bin/storage --namespace test upgrade --no-quickstart.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14442