Remove Pre-Merge Tests from `simulators/eth2/engine`, `simulators/ethereum/engine`

[marioevz]

Pre-Merge tests are no longer relevant to the clients and some of them are actively removing code related to Proof-of-work, clique, and other pre-PoS consensus algorithms.

These tests will eventually fail for all clients due to the code removal, so it's just appropriate to remove them from all simulators, to reduce run time, and simplify test code in general.

### Tasks
- [x] Remove Pre-Merge, and Merge transition tests from `simulators/ethereum/engine`
- [ ] Remove Pre-Merge, and Merge transition tests from `simulators/eth2/engine`
- [ ] Start all or most tests from Shanghai/Cancun fork to reduce run time in `simulators/eth2/engine`
- [x] Generalize `simulators/ethereum/engine` Engine API tests to work on any fork (currently they are tied to a specific fork, but failures can occur on any fork after Paris)

More details:

• simulators/ethereum/engine/suites/engine/tests.go
  • All Invalid Transition tests must be removed since they all start from Pre-Merge and tests the PoW->PoS transition
  • If a test verifies that invalid payloads are rejected, they should test the scenario on a purely PoS environment
  • TTD must be zero for all tests.
• Test suite simulators/ethereum/engine/suites/transition should be removed entirely.

[marioevz]

Bullet point 4 was completed by #840

Bullet points 2 and 3 will be completed by #838