Remove coverage hack from Karma
What does this MR do?
gitlab-foss!9133 (merged) introduced a hack to include files with 0% test coverage in the generated report. Given that we are migrating from Karma to Jest (&895 (closed)) and the hack causes trouble (#37799 (closed)), we are removing it here.
In Jest, we don't need this hack because there is the collectCoverageFrom
config option.