python: more robust handling of %timeit in notebooks

* python/tests/ipnbdoctest.py: Simply ignore %timeit blocks.

python/tests/ipnbdoctest.py

@@ -70,9 +70,6 @@ def sanitize(s):
     # normalize graphviz version
     s = re.sub(r'Generated by graphviz version.*', 'VERSION', s)
 
-    # ignore %timeit results
-    s = re.sub(r'^[0-9]+ loops, best of 3:.*per loop', '', s)
-
     # SVG generated by graphviz may put note at different positions
     # depending on the graphviz build.  Let's just strip anything that
     # look like a position.
@@ -214,7 +211,7 @@ def test_notebook(nb):
     errors = 0
     for ws in nb.worksheets:
         for i, cell in enumerate(ws.cells):
-            if cell.cell_type != 'code':
+            if cell.cell_type != 'code' or cell.input.startswith('%timeit'):
                 continue
             try:
                 outs = run_cell(kc, cell)