[Fix] Remove redundant cookies serialization from ProxyMixin

ProxyMixin.serialize referenced self.cookies but ProxyMixin doesn't
define it — relying on CookieMixin being in the MRO. This would crash
if ProxyMixin were composed without CookieMixin. The block was also
redundant since CookieMixin.serialize already handles cookies.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Adam Dobrawy

python_anticaptcha/tasks.py

@@ -49,8 +49,6 @@ def serialize(self, **result):
         if self.proxyLogin:
             data["proxyLogin"] = self.proxyLogin
             data["proxyPassword"] = self.proxyPassword
-        if self.cookies:
-            data["cookies"] = self.cookies
         return data