refactor(zetacore): delete ballots after maturity (#2863)

* add function to clear ballots

* add unit tests

* refactor abci tests

* refactor generate voter list method

* refactor names for ballot list functions

* refactor ClearMaturedBallots to ClearMaturedBallotsAndBallotList

* make getMaturedBallotHeight private

* make getMaturedBallotHeight private

* add migration script to delete ballots and tests with mainnet data

* add test for migration

* add a query for all ballots

* generate files

* add changelog

* fixed test naming

* update migration comment

* update module version

* make changes for comments 2

* remove max limit for Ballots query

* remove BallotDeleteEvent

* remove BallotDeleteEvent

changelog.md

@@ -8,6 +8,12 @@
 
 ## v25.0.0
 
+## Unreleased
+
+## Refactor
+
+* [2863](https://github.com/zeta-chain/node/pull/2863) - refactor zetacore to delete matured ballots and add a migration script to remove all old ballots.
+
 ### Features
 
 * [3235](https://github.com/zeta-chain/node/pull/3235) - add /systemtime telemetry endpoint (zetaclient)