[pkg] depends on cubicweb[crypto] instead of depending directly on pycrypto

Since we don't use Crypo module directly.

cubicweb_forgotpwd/__pkginfo__.py

@@ -20,8 +20,7 @@ classifiers = [
     'Programming Language :: JavaScript',
     ]
 
-__depends__ = {'cubicweb': '>= 3.25.0',
-               'pycrypto': None,
+__depends__ = {'cubicweb[crypto]': '>= 3.25.0',
                'Pillow': None,
                'six': None,
                }