Remove validate_email

[PrimozGodec]

Dependency validate_email is old and not maintained. It is used in pubmed.py and I think it is not required. Those two lines can be just omitted:

orange3-text/orangecontrib/text/pubmed.py

Lines 172 to 173 in fe04e1c

	if not validate_email(email):
	raise ValueError('{} is not a valid email address.'.format(email))

We should consider removing it.