[Extensions] Remove //chrome/common/extensions/docs

The old server and all its content have been removed. Clean up the
directory as a final step.

Bug: 1161364
Change-Id: Ice2ee9a6be566072575367e0598f4e884dd12807
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2613559
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Auto-Submit: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841063}

chrome/common/extensions/docs/.gitignore

-.sass-cache

chrome/common/extensions/docs/OWNERS

-# For documentation.
-mkearney@chromium.org
-
-# For webview documentation.
-file://components/guest_view/OWNERS
-
-# For devtools documentation.
-paulirish@chromium.org
-pbakaus@chromium.org
-
-# For server related things (Python, JavaScript, templates, etc).
-rockot@google.com

chrome/common/extensions/docs/README

---------
-Overview
-
-This is the content and its server for the extensions/apps documentation served
-from http://developer.chrome.com/(extensions|apps).
-
-Documentation for apps and extensions are partly generated from API definitions
-(for the reference material), and partly hand-written.
-
-All documentation sources are checked into source control, just like any other
-Chrome source code. The server consumes these sources and generates the
-documentation web pages dynamically.
-
-The goals of this system are:
-
-* Docs are generated from API definitions; it isn't possible to add or modify
-  APIs without creating stub reference documentation at the same time.
-
-* Docs are editable by anyone with Chrome commit access. This encourages
-  developers to do their part to keep doc up to date, and allows part-time
-  contributors to help too.
-
-* Docs go live automatically and immediately, upon check-in. There's no separate
-  push process for docs.
-
-* Docs are branched automatically with Chrome's source code; the docs for each
-  Chrome release are kept with the corresponding source code.
-
-* Users can always find the current doc for any Chrome release channel (i.e.,
-  /trunk/extensions/, /beta/apps/, etc.). These URLs are updated automatically
-  with Chrome's release process.
-
-
-------------
-Editing docs
-
-  1. Edit files.
-
-     - If you are not updating the static HTML for a docs page, you will most
-       likely not have to do anything. The docs server will automatically pick
-       up changes to the JSON or IDL schemas.
-
-     - Otherwise, they will be in chrome/common/extensions/docs/templates/.
-       See the "Overview of directories" section for more information.
-       Chances are you'll want to change a file in either "intros" (if changing
-       API documentation) or "articles" (if changing non-API documentation).
-       If adding files or APIs you'll also need to add something to "public".
-
-     - Files in templates directory use the Motemplate template language. It is
-       extremely simple, essentially: write HTML.
-       See third_party/motemplate/README.md.
-
-     - static/css/out/site.css is generated by compiling static/sass/*.scss
-       files. Don't change site.css directly. Instead, change the *.scss files
-       and run compass from this (docs/) directory:
-           compass compile .
-       See http://compass-style.org/install to install compass.
-       See https://codereview.chromium.org/238303002/#msg6 for configuration
-       information (config.rb).
-
-  2. Run 'server2/preview.py'
-
-  3. Check your work at http://localhost:8000/(apps|extensions)/<doc_name>
-
-  4. Commit files as with any other Chrome change. The live server will update
-     within 5-10 minutes.
-
-
------------------------
-Overview of directories
-
-* examples: The source for the sample extensions. Note that the sample apps are
-  checked into github at https://github.com/GoogleChrome/chrome-app-samples.
-
-* server2: The Python AppEngine server which serves all the content (living at
-  developer.chrome.com). Unless you're developing the server itself, you won't
-  need to worry about this (and if you are, see the README in there).
-
-* static: The static content (images, CSS, JavaScript, etc).
-
-* templates: These are the templates that server2 interprets and generates HTML
-  content with. This has four subdirectories:
-    - intros: The static content that appears before the API reference on API
-              pages.
-    - articles: The static content that appears on non-API pages.
-    - public: The top level templates for all pages.
-    - private: Helper templates used in rendering the docs.
-
-
---------------------
-The AppEngine server
-
-See server2/README.