CI: Run all tests when coverage is enabled ...

A recent change in the CI enabled coverage, however it did so on
the latest tags, meaning we were no longer running the other
tests (from the testsuite). This corrects it.

Build the tests and binary with -cov on POSIX ...

The CI was sending empty coverage reports because nothing
was being generated, as the variable was always false.
In the process, a bit of dead code was removed.

CI: Move single checks to Github, remove dead code ...

Remove support for very old frontend - we were not testing it anyways.
Move the useful checks to another job so they run once.

Remove internal mentions to Travis