minor fixes of pubmed engine

Closes #1045

searx/url_utils.py

@@ -3,7 +3,6 @@ from sys import version_info
 if version_info[0] == 2:
     from urllib import quote, quote_plus, unquote, urlencode
     from urlparse import parse_qs, parse_qsl, urljoin, urlparse, urlunparse, ParseResult
-    from urllib2 import urlopen
 else:
     from urllib.parse import (
         parse_qs,
@@ -17,7 +16,6 @@ else:
         urlunparse,
         ParseResult
     )
-    from urllib.request import urlopen
 
 
 __export__ = (parse_qs,