pgroonga: Remove now-unnecessary 'GRANT USAGE' statement.

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.

(cherry picked from commit dc2726c814)

tools/setup/postgresql-init-dev-db

@@ -108,7 +108,6 @@ EOF
 
 "${ROOT_POSTGRES[@]}" -v ON_ERROR_STOP=1 -e "$DBNAME_BASE" <<EOF
 CREATE EXTENSION pgroonga;
-GRANT USAGE ON SCHEMA pgroonga TO $USERNAME;
 EOF
 
 psql -v ON_ERROR_STOP=1 -e -h localhost postgres "$USERNAME" <<EOF