chore(issues): Remove usage of streamline-targeting-context flag from the backend

[leeandher]

Follow up PR to #64819 to remove the feature flag, associated tests and references to it.

[github-actions[bot]]

🚨 Warning: This pull request contains Frontend and Backend changes!

It's discouraged to make changes to Sentry's Frontend and Backend in a single pull request. The Frontend and Backend are not atomically deployed. If the changes are interdependent of each other, they must be separated into two pull requests and be made forward or backwards compatible, such that the Backend or Frontend can be safely deployed independently.

Have questions? Please ask in the #discuss-dev-infra channel.

[codecov[bot]]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (4dc9c8b) 81.40% compared to head (343401d) 81.39%. Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #64876      +/-   ##
==========================================
- Coverage   81.40%   81.39%   -0.01%     
==========================================
  Files        5252     5252              
  Lines      232201   232187      -14     
  Branches    45595    45588       -7     
==========================================
- Hits       189023   189000      -23     
- Misses      37292    37298       +6     
- Partials     5886     5889       +3     

Files	Coverage Δ
src/sentry/api/endpoints/codeowners/__init__.py	90.41% <100.00%> (-0.38%)	:arrow_down:
src/sentry/api/endpoints/codeowners/index.py	94.33% <100.00%> (-0.40%)	:arrow_down:
.../sentry/api/serializers/models/projectownership.py	100.00% <100.00%> (ø)
src/sentry/apidocs/examples/project_examples.py	100.00% <ø> (ø)
src/sentry/conf/server.py	88.18% <ø> (ø)
src/sentry/features/__init__.py	100.00% <ø> (ø)
src/sentry/api/endpoints/project_ownership.py	91.21% <90.00%> (-0.84%)	:arrow_down:
...entry/integrations/slack/message_builder/issues.py	89.72% <57.14%> (+0.24%)	:arrow_up:
src/sentry/notifications/utils/participants.py	91.53% <57.14%> (-0.04%)	:arrow_down:

... and 8 files with indirect coverage changes

[sentry-io[bot]]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ AttributeError: 'NoneType' object has no attribute 'startswith' /api/0/projects/{organization_slug}/{project_sl... View Issue

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[getsentry-bot]

revert failed (conflict? already reverted?) -- check the logs

[getsentry-bot]

revert failed (conflict? already reverted?) -- check the logs