test: fix sqlite indexer test

Had an import psycopg2 that was not neded or used. It shouldn't
have been there. Probbly bad copy/paste.

Also remove @skip_postgres that isn't needed now.

Author: rouilj

test/test_indexer.py

@@ -734,13 +734,10 @@ def test_query_errors(self):
         error = 'Query error: syntax error near "^"'
         self.assertEqual(str(ctx.exception), error)
 
-    @skip_postgresql
     def testNullChar(self):
        """Test with null char in string. FTS will throw
           an error on null.
        """
-       import psycopg2
-
        string="\x00\x01fred\x255"
        self.dex.add_text(('test', '1', 'a'), string)
        with self.assertRaises(IndexerQueryError) as cm: