Remove `testType` test argument

[rhmdnd]

Last year we refactored the e2e test suite by separating parallel and serial tests into separate packages.

https://github.com/ComplianceAsCode/compliance-operator/pull/264

This reduce the amount of custom test runner code we needed to maintain, and instead relied on using different packages to invoke the tests.

Because of this, we no longer have a need for the testType argument in our test runner. We can remove it to simplify the code.