ci: remove getsentry-dispatch (#109427)

since selective testing shipped in sentry, the getsentry dispatch on PRs
is a massive bottleneck at 20+ minutes

since fast-revert is convenient we're opting to optimize for speed and
accepting the rare case of sentry-breaks-getsentry reverts needing to
happen

Author: joshuarli

.github/file-filters.yml

@@ -33,7 +33,6 @@ frontend_all: &frontend_all
   - added|modified: 'static/**/*.{less,json,yml,md,mdx}'
   - added|modified: '{vercel,tsconfig,biome,package}.json'
 
-# Also used in `getsentry-dispatch.yml` to dispatch backend tests on getsentry
 backend_dependencies: &backend_dependencies
   - 'requirements-*.txt'
   - 'pyproject.toml'