fix: revert "thread safe resume (#2018)" (#2027)

This reverts commit 9533be8.

Author: kumaraditya303

coverage/collector.py

@@ -374,14 +374,13 @@ def pause(self) -> None:
 
     def resume(self) -> None:
         """Resume tracing after a `pause`."""
+        for tracer in self.tracers:
+            tracer.start()
         if self.core.systrace:
             if self.threading:
                 self.threading.settrace(self._installation_trace)
             else:
                 self._start_tracer()
-        else:
-            for tracer in self.tracers:
-                tracer.start()
 
     def post_fork(self) -> None:
         """After a fork, tracers might need to adjust."""