Simplify local .phpcs.xml to an absolute minimum
There is barely any code in this repository anyway. Only one PHP file.
All these additional sniffs barely apply here, and make this rule set
hard to maintain.
The rule set appears so convoluted because this was (I believe) at some
point copied from the Wikibase extension.
This patch also fixes as many issues as possible (except one, which is
very much intentional).