Fix pseudo unique *(e.g. non-upmixed but unique)* `@icon` key to use **last value** only

This is from GM standards... GM **always** picks last value if there is a conflict... **not** the first. If we want a specific 45px size icon we're going to have to implement one and probably put in the prefix support portion from CI.

Refs:
* https://github.com/OpenUserJs/OpenUserJS.org/pull/129#issuecomment-45696640