[fix] actually move tx_check.cpp from libserver to libbitcoin consensus

Summary:
I messed up https://reviews.bitcoinabc.org/D5961, it is still on libserver
for the cmake build.

That was not really a problem until I came back to try and get D6256 done,
now that D6710 is landed.

Test Plan:

ninja check-all [with -DBUILD_BITCOIN_WALLET=OFF as well]

make check-recursive
./test/functional/test_runner.py [with --disable-wallet as well]

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D6789