Follow up from PR #30698 (comment #30698 (review)).
mining_basic
checks that a block with wall time is rejected when the previous block is MAX_FUTURE_BLOCK_TIME
in the future, then checks that a block just beyond the MAX_TIMEWARP
is also rejected.
This PR removes the first check, since they seem to be essentially checking the same thing twice.
Also incorporates the suggestion in #30698 (review) to reuse block
.