wikipedia: replace "w" alias with "wp"

The problem

Wikipedia module stole our previous the precious "w" alias which could be used for "weather" or something else.

The solution

Remove "w" alias from Wikipedia module.

Notes

21:19:56 <+dgw> Make an issue, I'll put it in 8

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P.S. c bad

[dgw]

OK um, "our" refers to a previous bot run by @xnaas, not an older version of Sopel/Willie/Jenni/Phenny :P

Anyway I'm going to flesh this out with the whole context: We'd like to replace the w alias with wp, to match with wiktionary's wt, and free up w for the much more common meaning of "weather", probably in sopel-modules.weather by @RustyBower.