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>

doc/src/sgml/spi.sgml

@@ -4397,7 +4397,7 @@ execq(text *sql, int cnt)
     SPI_finish();
     pfree(command);
 
-    return (proc);
+    return proc;
 }
 </programlisting>