Update references to contributor agreement [ci skip]

.github/PULL_REQUEST_TEMPLATE.md

@@ -14,6 +14,6 @@ or new feature, or a change to the documentation? -->
 ## Checklist
 <!--- Before you submit the PR, go over this checklist and make sure you can
 tick off all the boxes. [] -> [x] -->
-- [ ] I have submitted the spaCy Contributor Agreement.
+- [ ] I confirm that I have the right to submit this contribution under the project's MIT license.
 - [ ] I ran the tests, and all new and existing tests passed.
 - [ ] My changes don't require a change to the documentation, or if they do, I've added all required information.

CONTRIBUTING.md

@@ -140,17 +140,6 @@ Changes to `.py` files will be effective immediately.
 
 📖 **For more details and instructions, see the documentation on [compiling spaCy from source](https://spacy.io/usage/#source) and the [quickstart widget](https://spacy.io/usage/#section-quickstart) to get the right commands for your platform and Python version.**
 
-### Contributor agreement
-
-If you've made a contribution to spaCy, you should fill in the
-[spaCy contributor agreement](.github/CONTRIBUTOR_AGREEMENT.md) to ensure that
-your contribution can be used across the project. If you agree to be bound by
-the terms of the agreement, fill in the [template](.github/CONTRIBUTOR_AGREEMENT.md)
-and include it with your pull request, or submit it separately to
-[`.github/contributors/`](/.github/contributors). The name of the file should be
-your GitHub username, with the extension `.md`. For example, the user
-example_user would create the file `.github/contributors/example_user.md`.
-
 ### Fixing bugs
 
 When fixing a bug, first create an