Update the migration restart on plugin deactivation

[rrennick]

In #470 we added a safety fallback for sites that may have had a plugin which includes pre-3.0 action scheduler. While this is still possible the number of sites would be very small. AS is recreating the migration action every time a plugin is deactivated.

There are also edge cases where the site has difficulty in marking the migration as complete (eg. #979) and the action ends up creating a large number of failed actions which do not get purged.

We should add some logic to this to eliminate creating the action when it is unnecessary. An example would be check the registered versions to see if any pre-3.0.