Streamline the code for flagging warnings in the reports

When tests are run in STRICT mode, we check for any errors or warnings in the report.

We currently have two functions:

``test_utils.check_report`` https://github.com/EducationalTestingService/rsmtool/blob/main/rsmtool/test_utils.py#L767 checks for both errors and warnings

``collect_warning_messages_from_report`` https://github.com/EducationalTestingService/rsmtool/blob/main/rsmtool/test_utils.py#L737 once again collects warning messages.

The warnings that are excluded under ``check_report`` would still be flagged as errors by ``collect_warning_messages_from_report``.

We need to figure out why we have these two functions and streamline them.