Provisioning fails when the system username is 'zulip' because the
script attempts to run 'GRANT zulip TO "zulip"', which PostgreSQL
rejects as a circular dependency.
This change adds a conditional check to ensure the GRANT is only
attempted if the database username and system username differ.
The previous version of the script did not quote VAGRANTUSERNAME, which caused
an error when running the script if the username contained `-` or other characters
that affect the Postgres syntax. Fix this using double-quotes.
This was only necessary for PGroonga 1.x, and the `pgroonga` schema
will most likely be removed at some point inthe future, which will
make this statement error out.
Drop the unnecessary statement.
