fix: fix a linter error

Author: mitsuhiko

sentry_sdk/integrations/dedupe.py

@@ -18,6 +18,5 @@ def processor(event, exc_info):
                 exc = exc_info[1]
                 if last_seen.get(None) is exc:
                     return
-                seen = False
                 last_seen.set(exc)
                 return event