Remove Python2 references from the source code.

refs #5443

Initial patch: Neel Patel

web/pgadmin/utils/sqlautocomplete/sqlcompletion.py

@@ -9,13 +9,7 @@ from .parseutils.utils import (
 from .parseutils.tables import extract_tables
 from .parseutils.ctes import isolate_query_ctes
 
-PY2 = sys.version_info[0] == 2
-PY3 = sys.version_info[0] == 3
-
-if PY3:
-    string_types = str
-else:
-    string_types = basestring
+string_types = str
 
 
 Special = namedtuple('Special', [])