Remove coverage-test-on-main-scheduled

The job coverage-test-on-main-scheduled fails now, because the lcov command needs to be updated to handle the clang-18 format. However, the job provides the same coverage as ivas-conformance-linux but without tests/split_rendering/test_split_rendering.py. I suggest to remove this job, unless someone sees a need for it or if we want to test coverage of some other tests.

Pinging @kiene, @malenovskyvl, @pihlajakuja.