[MICROBA-1298]
* Remove a Segment certificate event that was, historically, only emit from the courseware.
The Segment event that was previously (only) issued in the courseware doesn't seem to be important or referenced anywhere we could see. Since this event only tracked certificate generation attempts from one (of multiple) paths to initiate certificate generation in v1, I didn't think the historical event data captured is complete. We approached our data teams and I determined this event was not of high importance. For this reason, I am suggesting we just stop using this event and remove the code responsible for sending it.
We will continue to track certificate creation/generation using the existing `edx.certificate.created` event.
[MICROBA-1208]
* consolidate `has_html_certificates_enabled` and `has_html_certificates_enabled_from_course_overview`, the latter of the two functions was created for use during our transition away from using the modulestore in the certificate app.
[MICROBA-1178]
- remove modulestore usage in `generation_handler.py`
- add duplicate functions that utilize a CourseKey or CourseOverview to remove dependence on modulestore (this will be cleaned up (if possible) at a later part of this refactor)
- add python API function to `content`/`course_overview` app that will retrieve a single CourseOverview (rather than a serialized list of dicts of CourseOverview data)
