Fix nits in unit tests

Summary:
Rename monolith_opcodes.cpp to monolith_opcodes_tests.cpp
Fix a typo in the boost test suite name in script_commitment_tests.cpp
Remove lcg.h from CMakeList

Test Plan:

make check
ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2495