Remove the import hook after successfully setting a breakpoint, instead of waiting until it is completed.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=138536493

Author: b-daniels

src/googleclouddebugger/python_breakpoint.py

@@ -208,6 +208,7 @@ def _TryActivateBreakpoint(self):
         condition,
         self._BreakpointEvent)
 
+    self._RemoveImportHook()
     return True
 
   def _FindCodeObject(self):