Remove design process document

We are moving the contents of apertis-designs over to the website. This
workflow will therefore be obsolete. Delete it now.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

content/guidelines/design_process.md

-+++
-date = "2016-12-19"
-weight = 100
-
-title = "Design Process"
-
-aliases = [
-    "/old-wiki/Guidelines/Design_process"
-]
-+++
-
-  - The design documents live in the
-    [apertis-designs](https://git.apertis.org/cgit/apertis-designs.git)
-    git repository.
-  - They are written in [hotdoc](https://github.com/hotdoc)
-  - …and published on <https://docs.apertis.org/>
-  - …with the long term aim of being moved to designs.apertis.org
-
-When writing a design document:
-
-1.  [Clone](https://git-scm.com/docs/git-clone) the
-    [apertis-designs](https://git.apertis.org/cgit/apertis-designs.git)
-    git repository.
-2.  [Work in a branch](https://git-scm.com/docs/git-branch) on your new
-    document (or if you're updating an existing document).
-3.  Create a file for the document in the /docs directory.
-      - If you are updating an existing document, update its version
-        number and edit it in place (don't create a new copy of it)
-4.  The document is reviewed in Phabricator following a similar process
-    to code review
-5.  Once you’ve incorporated review comments and the changes have been
-    approved by the reviewer, merge the branch to master