chore(alerts): Remove metric alert rate limiting flag

[isabellaenriquez]

Follow up to #60483

Closes #58648

[codecov]

Codecov Report

Merging #60487 (7e665c1) into master (bb1cbec) will increase coverage by 0.00%.
Report is 10 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #60487   +/-   ##
=======================================
  Coverage   80.87%   80.87%           
=======================================
  Files        5183     5183           
  Lines      227519   227496   -23     
  Branches    38251    38244    -7     
=======================================
- Hits       183996   183984   -12     
+ Misses      37901    37892    -9     
+ Partials     5622     5620    -2     

Files	Coverage Δ
src/sentry/conf/server.py	90.00% <ø> (ø)
src/sentry/features/__init__.py	100.00% <ø> (ø)
.../components/onboardingWizard/useOnboardingDocs.tsx	70.37% <ø> (-1.98%)	⬇️
...c/app/components/performanceOnboarding/sidebar.tsx	68.60% <ø> (+0.78%)	⬆️
...ProfilingOnboarding/profilingOnboardingSidebar.tsx	30.00% <ø> (ø)
...tatic/app/components/replaysOnboarding/sidebar.tsx	26.53% <ø> (+0.53%)	⬆️

... and 6 files with indirect coverage changes