remove incorrect block gossip validation condition

[tersec]

This was excessively aggressive and could cause a deadlock in recovery of EL sync verification.

It was an implementation of https://github.com/ethereum/consensus-specs/blob/dev/specs/bellatrix/p2p-interface.md#beacon_block:

• If exection_payload verification of block's parent by an execution node is not complete:
  • [REJECT] The block's parent (defined by block.parent_root) passes all validation (excluding execution node verification of the block.body.execution_payload).

However, because Nimbus always completes execution_payload verification by the time a block reaches the DAG, this can't ever happen. The first thing Nimbus does is to ask the EL, and wait for the EL's reply either ACCEPTED or SYNCING, because optimistic sync requires this anyway. So by the time it reaches here, the only relevant condition is

• otherwise:
  • [IGNORE] The block's parent (defined by block.parent_root) passes all validation (including execution node verification of the block.body.execution_payload).

which is already handled.

[github-actions]

Unit Test Results

       12 files  ±0       860 suites  ±0   1h 4m 10s ⏱️ - 1m 3s
  1 982 tests ±0    1 835 ✔️ ±0  147 💤 ±0  0 ❌ ±0 
10 662 runs  ±0  10 472 ✔️ ±0  190 💤 ±0  0 ❌ ±0 

Results for commit 61e57e6. ± Comparison against base commit b60456f.