Summary:
Major YSQL upgrade involves a soft delete and recreate of the databases during pg_upgrade. Normally drop database is blocker if the database is under xCluster.
This only affects the `yugabyte` and internal dbs created during the initdb phase.
Relaxing this check for the major upgrade since no real database is dropped.
Jira: DB-17092

Test Plan: TEST_P(XClusterUpgradeTest, UpgradeHashPartitionedTable) {

Reviewers: slingam

Reviewed By: slingam

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D44673