[coverage] Remove subtrees and benchmarks from coverage report
Removes stats about leveldb, univalue, and benchmark coverage from the coverage reports. Since we don't test these three items specifically and thus don't care about test coverage for these items. This builds on top of #10511 to use the faster lcov -r replacement.
Backport of core PR10565 and PR11443
Depends on D3565
../configure --enable-lcov make make cov
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D3545