ref(profiler): Remove dead code in run() cleanup

Remove the no-op `buffer = None` assignment on a local variable before
the function returns. Setting a local variable to None provides no GC
benefit since it goes out of scope immediately after.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: ericapisani

sentry_sdk/profiler/continuous_profiler.py

@@ -439,7 +439,6 @@ def run(self) -> None:
         buffer = self.buffer
         if buffer is not None:
             buffer.flush()
-            buffer = None
 
 
 class ThreadContinuousScheduler(ContinuousScheduler):