Remove unnecessary parentheses in return statements

The parenthesized style has only been used in a few modules.  Change
that to use the style that is predominant across the whole tree.

Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Reviewed-by: Ryan Murphy <ryanfmurphy@gmail.com>

contrib/spi/refint.c

@@ -636,5 +636,5 @@ find_plan(char *ident, EPlan **eplan, int *nplans)
 	newp->splan = NULL;
 	(*nplans)++;
 
-	return (newp);
+	return newp;
 }