In most affected tests, the backend diagnostic such as "conflicting JVM
signature" or "accidental override" is directly caused by some already
existing error reported by frontend, so it doesn't make sense to check
backend diagnostics there.
Tests where that was not the case were moved/copied to
`testsWithJvmBackend`.
There was a refactoring of AbstractDiagnosticsTest in 9052ef06 which
contains bug that `setupEnvironment` for AbstractDiagnosticsTestUsingJavac
was not called, so for last year tests `UsingJavac` had no difference
with usual diagnostics tests which causes some contradictions in test data
Alexander Udalov