Revert full GC collect

based on suggestion from code review

Author: richardsheridan

lib/matplotlib/_pylab_helpers.py

@@ -66,7 +66,10 @@ def destroy(cls, num):
             manager.canvas.mpl_disconnect(manager._cidgcf)
         manager.destroy()
         del manager, num
-        gc.collect()
+        # Full cyclic garbage collection may be too expensive to do on every
+        # figure destruction, so we collect only the youngest two generations.
+        # see: https://github.com/matplotlib/matplotlib/pull/3045
+        gc.collect(1)
 
     @classmethod
     def destroy_fig(cls, fig):