Remove the redundant signature recovery and hash

[wanderingbort]

Before applying blocks, we add them to fork-db. Only if fork-db signals better header-validated fork do we bother to apply the block. As part of header-validation we validate the signature therefore, the additional check in ::apply_block is wasteful.

Actually, we need at least a check to make sure the pending block header is identical to the signed block header, otherwise a producer could falsify the action merkle root, for example.

[heifner]

Need to update tests:

/data/job/unittests/forked_tests.cpp(131): �[4;31;49mfatal error: in "forked_tests/fork_with_bad_block": exception fc::exception expected but not raised

Failure occurred in a following context:

    Testing Fork: 0�[0;39;49m

�[33m0 exception: unspecified

rethrow

    {}

    thread-0  forked_tests.cpp:142 test_method�[0m

/data/job/unittests/main.cpp(15): �[4;31;49mfatal error: in "forked_tests/fork_with_bad_block": Caught Unexpected Exception�[0;39;49m

[wanderingbort]

@heifner I think those were legit regressions that should now be fixed (without changing the tests)

hopefully resolved with d2699c0

[heifner]

@wanderingbort Tests doing their jobs, nice.