resourceloader: Remove elaborate dom-based console shim

resourceloader: Remove elaborate dom-based console shim

This was a hack loosely inspired by Firebug Lite, that essentially
created a footer toolbar like the one from "mediawiki.debug", and
write console messages to it, if the browser doesn't have a console
natively.

We don't currently support any browsers in JS-mode that don't have
a console feature of some kind.

I'm keeping the file for now, because it is still useful for
mw.log (not to be confused with mw.log.warn or mw.log.error) to
not do anything in production mode by default. This because there
can be significant overhead from writing to real console object,
regardless of the fact that it isn't visible in browsers by default.

Test Plan:
* Both before and after this commit,
  - On a normal page view, `mw.log("msg")` does nothing when run
    from the browser console.
  - On a page with ?debug=true, `mw.log("msg")` acts
    like `console.log("msg")` would.

Bug: T192623
Change-Id: Ifc8dd91f473c9235e1d4e27c202c97802530a272