Update deprecation procedure in TCW 27

[trishaoconnor]

Update the deprecation procedure in TCW 27 to detail precisely what needs to be deleted after the deprecation date has been set.

I've included some bullet points as a rough checklist below of what needs to be deleted when an element is deprecated. If I've omitted or misunderstood anything, please feel free to correct or add to this list.

On the date of deprecation or the day after, complete the following:

• Delete all the references to the element in the examples,
• Delete all the references to the element in the prose,
• Delete the spec file and the place where it is in the repo
• Delete the spec desc,
• Delete the include,

Suggestion: Perhaps check out a branch a few days before the deprecation date for these changes and then merge it on the day of deprecation. Maybe create a pull request so that someone could review the work prior to merging?