Remove redundant files

[woutermont]

This PR removes some redundant files from the repo. As far as I know, these files do not contain relevant content, and they are not used by or refered to from any other file in the repo. Also keep in mind that this is a git repo, and so these files are not lost; if need be, we can easily restore them.

• .default-acl: No idea what this is. It is not even a real ACL file. Maybe @ericprud knows.
• diff-20111123.html: Some very old HTML file, probably meant as a diff to or from the draft back then (which is stored in the drafts folder). It's not a real diff file though, and its formatting is completely messed up, so comparing is not possible.
• style.css & W3C-ED.css: Both are (old) copies from the ReSpec and W3C stylesheets. All HTML files in the repo (even the drafts) use their online version though (or embeded CSS).

[melvincarvalho]

Good idea, thanks. They all look defunct.

[jacoscaz]

/chair hat off

+1 from me

[jacoscaz]

Any objection to this PR?

[jacoscaz]

Any objection to this PR? Just making sure...

[jacoscaz]

Thank you @woutermont !