Unnecessary NameError exception handling in tutor.py

[ievacerny]

Previous implementation of tutor.py (#697) raised a NameError in main() if "no tutorials were found". Current implementation (#712) will open any folder and attempt to show the contents -- no error is raised and therefore no exception handling is needed.

traitsui/examples/tutorials/tutor.py

Lines 47 to 51 in 3e2ce86

	try:
	main(root_dir)
	except NameError as e:
	print(e)
	print(usage)