Bug #149: Deletion of unnecessary checks before a few calls of cURL functions

The following functions return immediately if a null pointer was passed.
* Curl_cookie_cleanup
* curl_formfree

It is therefore not needed that a function caller repeats a corresponding check.

This issue was fixed by using the software Coccinelle 1.0.0-rc24.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>