Actually, remove retype from dev dependencies.

If retype gets vendored in an upstream tool, then we won't be needing it
here. Better not clutter up the dev dependencies with things we are not
currently needing.

Pipfile

@@ -9,4 +9,3 @@ python_version = "3.6"
 [packages]
 
 [dev-packages]
-retype = {editable = true, git = "git@github.com:TypedDjango/retype.git"}