Re-enable coveralls code coverage by adding coveralls action to github actions workflow

[jwlodek]

• Remove unused travis ci configuration file
• Update github actions CI configuration to re-enable coveralls code coverage metrics

[jwlodek]

This appears to have worked:

[jwlodek]

I've moved the coverage check to the matrix job that builds against adsupport, to guarantee that most dependency libraries are available - I noticed that on the default ubuntu-latest/os/default the lz4 and bslz4 tests in the Codec tests did not get covered, presumably since there isn't a bitshuffle OS package.

[jwlodek]

Hmm, now it picked up those branches in the Codec tests, but I don't seem to get .gcda files for all of the files I'd expect (e.g. ADDriver.cpp is not listed). The previous run listed 59 files, the new one only 37. Need to investigate further.