ref(ddm): Clean up unused options and feature flags

[iambriccardo]

This PR removes some unused feature flags and options that were needed for DDM.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.02%. Comparing base (dd70023) to head (77ab399).
Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #70736      +/-   ##
==========================================
- Coverage   80.02%   80.02%   -0.01%     
==========================================
  Files        6505     6503       -2     
  Lines      290784   290644     -140     
  Branches    50109    50087      -22     
==========================================
- Hits       232710   232592     -118     
+ Misses      57637    57615      -22     
  Partials      437      437              

Files	Coverage Δ
src/sentry/conf/server.py	89.42% <ø> (ø)
src/sentry/options/defaults.py	100.00% <ø> (ø)

... and 25 files with indirect coverage changes

[shellmayr]

The flag 'custom-metrics-experimental' seems to be used in quite some parts of the front-end through hasMetricsExperimentalFeature - should this be cleaned up together?

[iambriccardo]

The flag 'custom-metrics-experimental' seems to be used in quite some parts of the front-end through hasMetricsExperimentalFeature - should this be cleaned up together?

Good catch, I forgot frontend uses options with implicit organizations: prefix.