chore(metrics): drop the dead billed_teams_count gauge (firecrawl#4011)

The gauge read scard("billed_teams"). That set's feeders were removed
(firecrawl#3992) and its drain — the index-worker tally loop — is removed in firecrawl#4010,
so the set is permanently empty and the gauge reported a constant 0. Its
"billed but not yet tallied" label describes a pipeline that no longer
exists (Autumn is the source of truth for credits), so it was misleading.

Co-authored-by: firecrawl-spring[bot] <254786068+firecrawl-spring[bot]@users.noreply.github.com>
Co-authored-by: micahstairs <micah@sideguide.dev>

Author: firecrawl-spring[bot]

apps/api/src/controllers/v0/admin/metrics.ts

@@ -41,10 +41,6 @@ concurrency_limit_queue_job_count_total ${totalJobCount}
 # TYPE concurrency_limit_queue_team_count gauge
 concurrency_limit_queue_team_count ${teamCount}
 
-# HELP billed_teams_count The number of teams that have been billed but not yet tallied
-# TYPE billed_teams_count gauge
-billed_teams_count ${await getRedisConnection().scard("billed_teams")}
-
 ${nuqGetLocalMetrics()}
 ${semaphoreMetrics}`);
 }