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>

src/interfaces/ecpg/test/expected/preproc-variable.c

@@ -272,5 +272,5 @@ if (sqlca.sqlcode < 0) exit (1);}
 #line 98 "variable.pgc"
 
 
-	return (0);
+	return 0;
 }