fix(ci): remove unused isWithinReplayWindow import in pagerduty signal source

Lint failure (@typescript-eslint/no-unused-vars). The pagerduty replay-window
check itself is tracked as a residual review finding (P1) for follow-up.

packages/dashboard/src/signal-sources/pagerduty.ts

@@ -1,6 +1,5 @@
 import {
   applySignalCaps,
-  isWithinReplayWindow,
   verifyHmacSignature,
   type Signal,
   type SignalSeverity,