Remove the GAIA ID column from the User table (#2172)

The field has already been removed from the Java code base in #2170.

db/src/main/resources/sql/flyway/V147__drop_gaia_id_from_user.sql

@@ -0,0 +1,16 @@
+-- Copyright 2023 The Nomulus Authors. All Rights Reserved.
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+ALTER TABLE "User" DROP COLUMN gaia_id;
+