How to permanently disable http_proxy
Solution 1:
Make sure that those variables are not declared in any of the below files:
~/.bashrc/etc/bash.bashrc/etc/environment
If they are, it'd be better if you remove those lines.
However, if you're unable to find them, then put the unset lines you've mentioned in your ~/.bashrc file.
Solution 2:
Be sure to change the method dropdown from "manual" to "none". This will erase everything - you may need to restart the machine after doing this.