[Python] Don't check metakernel availablility in nbdiff.py

This is redundant. The `root` Python kernel itself should give a good
error is `metakernel` is not available.

Author: guitargeek

python/JupyROOT/nbdiff.py

@@ -187,12 +187,6 @@ def isInputNotebookFileName(filename):
         raise ImportError("Cannot import jupyter")
 
     kernelName = getKernelName(nbFileName)
-    if kernelName == 'root':
-        try:
-            # We need metakernel for ROOT C++ notebooks
-            import metakernel
-        except:
-            raise ImportError("Cannot import metakernel")
 
     retCode = canReproduceNotebook(nbFileName, kernelName, needsCompare)
     sys.exit(retCode)