ref(seer grouping): Stop sending/receiving group id when communicating with Seer

[lobsterkatie]

Now that Seer has stopped expecting group ids (we started sending the hash in addition to group id in #70244, and seer switched to handling hash rather than group id in https://github.com/getsentry/seer/pull/625), and has stopped sending them back (also changed in https://github.com/getsentry/seer/pull/625), we can close the loop and stop sending or expecting them on the Sentry side, too.

This PR makes that change, which allows for some simplification in three places:

• In the SimilarIssuesEmbeddingsRequest and RawSeerSimilarIssueData types, group_id and parent_group_id (respectively) are removed and hash and parent_hash (respectively) are no longer optional.

• In SeerSimilarIssueData.from_raw, we no longer have to play the "Did Seer send back parent hash or parent group id?" game, and can instead just trust that the parent hash will be there and process it.

• In GroupSimilarIssuesEmbeddingsEndpoint.get_formatted_results, we no longer have to handle the case of there being parent group ids in the passed data which correspond to non-existent groups, since the group ids there are no longer coming from Seer but from us, which gives us the opportunity to make sure they're real before passing them on. (Technically this could/should have happened in ref(seer-grouping): Automatically convert RawSeerSimilarIssueData into SeerSimilarIssueData #70240, but better late than never.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.88%. Comparing base (da94b69) to head (e4f5880).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #70396   +/-   ##
=======================================
  Coverage   77.88%   77.88%           
=======================================
  Files        6528     6528           
  Lines      290835   290824   -11     
  Branches    50338    50335    -3     
=======================================
- Hits       226518   226510    -8     
+ Misses      58070    58065    -5     
- Partials     6247     6249    +2     

Files	Coverage Δ
...y/api/endpoints/group_similar_issues_embeddings.py	100.00% <ø> (ø)
src/sentry/seer/utils.py	93.15% <100.00%> (-0.48%)	⬇️

... and 6 files with indirect coverage changes