Avoid getThis() usages in zip extension

There isn't any magic going on here, we can just use ZEND_THIS
and assume it exists.

ext/zip/php_zip.c

@@ -2884,15 +2884,11 @@ static void _php_zip_progress_callback(zip_t *arch, double state, void *ptr)
 PHP_METHOD(ZipArchive, registerProgressCallback)
 {
 	struct zip *intern;
-	zval *self = getThis();
+	zval *self = ZEND_THIS;
 	double rate;
 	zval *callback;
 	ze_zip_object *obj;
 
-	if (!self) {
-		RETURN_FALSE;
-	}
-
 	if (zend_parse_parameters(ZEND_NUM_ARGS(), "dz", &rate, &callback) == FAILURE) {
 		return;
 	}
@@ -2942,14 +2938,10 @@ static int _php_zip_cancel_callback(zip_t *arch, void *ptr)
 PHP_METHOD(ZipArchive, registerCancelCallback)
 {
 	struct zip *intern;
-	zval *self = getThis();
+	zval *self = ZEND_THIS;
 	zval *callback;
 	ze_zip_object *obj;
 
-	if (!self) {
-		RETURN_FALSE;
-	}
-
 	if (zend_parse_parameters(ZEND_NUM_ARGS(), "z", &callback) == FAILURE) {
 		return;
 	}