Undeploying a MIGRATION change should leave it as inactive in the deploylog table, instead of deleting it

[shantstepanian]

Expected Behavior

When a migration change is dropped, it should be left as inactive in the DB. This is desirable for a couple reasons:

1. if it were accidentally added back later, we do not try to redeploy it
2. so that we can diagnose issues later on if it were dropped in the past

Actual Behavior

Today, the migration change is deleted, leaving the risk of re-deploying it

Obevo Version where this issue was observed

6.4.0

Steps to reproduce the behavior

Use case 1: Step 1- deploy migration change Step 2- new version w/ migration deleted Step 3- new version w/ migration added back with same content; should be no-op

Use case 2: Step 3- new version w/ migration added back with different content; should throw exception