nix(loadtest): remove jwt-cache-worst

This test is not really functional (anymore?). It depends on some tokens
expiring - but they don't, really. This is because:
1) Before merging the RSA and HS variants earlier in this patch series,
they ran roughly 15s and 34s respectively in CI.
2) Since PostgREST takes a clock skew of up to 30 seconds into account,
there would be *at most* 4s of expiring tokens in a test run - and
*only* in the HS case, not for RSA.

.github/workflows/test.yaml

@@ -131,7 +131,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        kind: ['mixed', 'jwt-cache', 'jwt-cache-worst']
+        kind: ['mixed', 'jwt-cache']
     name: Loadtest
     runs-on: ubuntu-24.04
     steps: