Revert "test: _via_set_trace_frame"

This reverts commit 92b3ee6aa3.

Lib/bdb.py

@@ -199,10 +199,9 @@ class Bdb:
 
     def stop_here(self, frame):
         "Return True if frame is below the starting frame in the stack."
-        if (
-            self.stopframe is None
-            and getattr(self, "_via_set_trace_frame", frame) == frame
-        ):
+        if (self.stopframe is None
+                and self.returnframes is None
+                and self.stoplineno == 0):  # TEST: via set_step
             return True
         if self.skip and \
                self.is_skipped_module(frame.f_globals.get('__name__')):
@@ -328,7 +327,6 @@ class Bdb:
         """
         if frame is None:
             frame = sys._getframe().f_back
-        self._via_set_trace_frame = frame
         self.reset()
         while frame:
             frame.f_trace = self.trace_dispatch