Revert "Add lint checks for WYSIWYG extension"

According to https://www.mediawiki.org/wiki/Extension:WYSIWYG this is
no more maintained on our Gerrit install.

This reverts commit 5d96e1a90a00d9a4eeb6d7c9f7b54bcda5cec895.

Change-Id: I78fcb84c2f5ab1d87b2b31a49d00f33c2bdec0a3