Remove `RewardsManager.sol`

[MikeHathaway]

Description

• Removed RewardsManager.sol and all respective tests
• Unwound RewardsManager invariants with PositionManager invariants

Purpose

During our Sherlock and Kiril audits there was a bug discovered in RewardsManager.sol. Although we had previously agreed not to deploy the contract prior to the audit, having a implementation example with a bug is a bad idea. We opted to remove RewardsManager.sol all together in the event someone used it.

Impact

Tasks

• [x] Changes to protocol contracts are covered by unit tests executed by CI.
• [x] Protocol contract size limits have not been exceeded.
• [x] Gas consumption for impacted transactions have been compared with the target branch, and nontrivial changes cited in the Impact section above.
• [x] Scope labels have been assigned as appropriate.
• [x] Invariant tests have been manually executed as appropriate for the nature of the change.

[ith-harvey]

Commit 9fd555c removes ERC20PoolPositionHandler and regression tests, which I spent substantial effort making operational.

Apologies @EdNoepel , didn't take the time to review "why" you made the changes. Your changes successfully resolved test_regression_index_out_of_bounds() and test_regression_max_less_than_min(). I added them again in this commit -> https://github.com/ajna-finance/contracts/pull/1041/commits/3a63048a77a381449fabc84c1175b6c8a677aeed

[ith-harvey]

I prefer to be consistent in naming, that is rename Positions directories in tests to PositionManager (to match ERC20Pool and ERC721Pool namings)

Resolved -> https://github.com/ajna-finance/contracts/pull/1041/commits/3a63048a77a381449fabc84c1175b6c8a677aeed