Ext-CSS rules with 'remove' don't work in apps at hotcleaner.com

[AdamWr]

Similar issue as here - https://github.com/AdguardTeam/ExtendedCss/issues/127

Steps to reproduce:

1. Use AdGuard app
2. Add this rule to user rules:

hotcleaner.com#$?#body { remove: true; }

3. Go here - https://www.hotcleaner.com/

Website should be blank, but extended CSS rules with remove do not work. I guess that it happens, because website override Element.prototype.remove and Element.prototype.removeChild function.

[ameshkov]

Relatively easy to fix, we should save reference to these functions.