feat: update IS database instantly, no more dependency on DIP0020

[knst]

Issue being fixed or feature implemented

Upgrade of IS database depends on activation of DIP0020. It's no more need because it is activated long time ago.

What was done?

Removed dependency of IS database upgrade on DIP0020. Also removed LOCK for ::mempool.cs which is not actually has been used inside GetTransaction during upgrade: no mempool -- no lock.

How Has This Been Tested?

Run unit and functional tests.

Breaking Changes

N/A

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation
• I have assigned this pull request to a milestone

[UdjinM6]

It's probably safe to just drop CInstantSendDb::Upgrade() completely

[knst]

It's probably safe to just drop CInstantSendDb::Upgrade() completely

It's easier to migrate than ask to reindex, I think. Is there are good API to tell that we need to reindex? I think it's easy only from init.cpp

[UdjinM6]

Good point re potential garbage leftover but we don't have to reindex because

1. unlike evodb isdb is a temporary one, can be dropped at any point and
2. pre-dip0020 IS locks are irrelevant now, we can ignore them

Check ada5948 b6c8844 (made a typo in commit title 🙈)

[UdjinM6]

utACK 89528bc

[PastaPastaPasta]

utACK 89528bc