refactor(crypto): make all Slots.* methods static

[faustbrian]

Summary

Make all methods of Crypto.Slots static as there was no access to instance properties or methods other then getMilestone which doesn't need to be a method. Also removed some methods that were not used throughout the packages or tests.

What kind of change does this PR introduce?

• Bugfix
• New feature
• Refactoring / Performance Improvements
• Build-related changes
• Documentation
• Tests / Continuous Integration
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

Does this PR release a new version?

• Yes
  • All tests are passing
  • All benchmarks are passing without any major regressions
  • Sync from 0 works on mainnet
  • Sync from 0 works on devnet
  • Starting a new network and forging on it work
  • Explorer is fully functional
  • Wallets are fully functional
• No

Checklist

• I have read the CONTRIBUTING documentation
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[codecov-io]

Codecov Report

Merging #2473 into develop will decrease coverage by 0.17%.
The diff coverage is 81.48%.

@@             Coverage Diff             @@
##           develop    #2473      +/-   ##
===========================================
- Coverage    67.85%   67.68%   -0.18%     
===========================================
  Files          386      400      +14     
  Lines         8402     8518     +116     
  Branches       438      440       +2     
===========================================
+ Hits          5701     5765      +64     
- Misses        2648     2698      +50     
- Partials        53       55       +2

Impacted Files	Coverage Δ
...database-postgres/src/repositories/transactions.ts	22.91% <ø> (ø)	⬆️
...ckages/core-p2p/src/socket-server/versions/peer.ts	76.92% <ø> (ø)	⬆️
...ackages/core-tester-cli/src/commands/make/block.ts	93.54% <ø> (ø)	⬆️
packages/core-forger/src/manager.ts	55.43% <0%> (ø)	⬆️
packages/core-p2p/src/network-state.ts	7.84% <0%> (ø)	⬆️
...es/core-api/src/versions/1/delegates/controller.ts	43.24% <0%> (ø)	⬆️
packages/crypto/src/blocks/block.ts	91.2% <100%> (ø)	⬆️
packages/crypto/src/crypto/slots.ts	100% <100%> (ø)	⬆️
packages/core-transaction-pool/src/processor.ts	77.46% <100%> (ø)	⬆️
...es/core-blockchain/src/utils/validate-generator.ts	100% <100%> (ø)	⬆️
... and 19 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3114e58...0415404. Read the comment docs.