Remove deprecated Heroku deployment strategies

Author: BanzaiMan

user/deployment/heroku.md

@@ -164,8 +164,6 @@ Travis CI supports different mechanisms for deploying to Heroku:
 
 - **api:** Uses Heroku's [Build API](https://devcenter.heroku.com/articles/build-and-release-using-the-api). This is the default strategy.
 - **git:** Does a `git push` over HTTPS.
-- **git-ssh:** Does a `git push` over SSH. This will generate a new key on every deployment.
-- **git-deploy-key:** Does a `git push` over SSH. It will reuse the same key on every deployment. This is only available for private projects.
 
 It defaults to **api**, but you can change that via the **strategy** option:
 
@@ -176,10 +174,6 @@ deploy:
   strategy: git
 ```
 
-> Note that the `git-ssh` and `git-deploy-key` strategies are **deprecated**, and will be shut
-> down on June 26th, 2017.
-> Please contact us if you have issues switching away from these.
-
 #### Using `.gitignore` on `git` strategy
 
 When you use any of the `git` strategies, be mindful that the deployment will