Remove the most recent staking migration

[4meta5]

Removes the migration from #757 and #748 and the associated tests. It also removes the hotfix_unreserve_nomination extrinsic and event.

It does NOT kill the storage bool, it just removes the type declaration from the code. There is a jira ticket to make a democracy proposal of frame_system::kill_storage call for the storage value FixBondLessMigrationExecuted.

[notlesh]

It's definitely not significant, but I wanted to point out that removing the storage item without deleting it will leave some junk in storage.

[notlesh]

Sorry, that Close button is way too close to the Comment button for me 😅

[4meta5]

It's definitely not significant, but I wanted to point out that removing the storage item without deleting it will leave some junk in storage.

Good point, I'd rather kill it. Inconveniently, now this requires a follow up migration to remove the on_runtime_upgrade block and storage bool.

[JoshOrndorff]

I'm not fully familiar with all the fixes and migrations that went in. But this PR definitely just removes them, and adds a migration to remove the previous migration flag.

[notlesh]

It's definitely not significant, but I wanted to point out that removing the storage item without deleting it will leave some junk in storage.

Good point, I'd rather kill it. Inconveniently, now this requires a follow up migration to remove the on_runtime_upgrade block and storage bool.

I say we remove through democracy using system -> killStorage()

[4meta5]

I say we remove through democracy using system -> killStorage()

Sure, we should make a jira ticket for it so we don't forget. It's nicer then because we can be done with this in 1 migration instead of 2.