Remove redundant tests that have no preconsensus or consensus

[GalRogozinski]

Description

Validator Registration doesn't have consensus or post consensus
Attester and Sync committees don't have preconsensus...

Yet they appear in various spectests that test different consensus/pre-consensus on them.
It should suffice to have a single spectest that proves that they don't run consensus/preconsenus.

In addition there are some duplicate tests.

Please review the following files:

• preconsensus/valid_msg.go
• consensus/future_msg.go
• consensus/past_msg.go
• pre_consensus_justifications/inconsisten_root_count.go
• pre_consensus_justifications/inconsisten_roots.go
• postconsensus/invalid_msg_slot.go