tox/ci: remove testing with pytest's features branch

pytest is using the master branch now only.

.appveyor.yml

@@ -7,7 +7,6 @@ environment:
   - TOXENV: "py37-pytestlatest"
   - TOXENV: "py38-pytestlatest"
   - TOXENV: "py38-pytestmaster"
-  - TOXENV: "py38-pytestfeatures"
 
 install:
   - C:\Python38\python -m pip install -U pip setuptools virtualenv

.travis.yml

@@ -46,8 +46,6 @@ jobs:
       env: TOXENV=py37-pytestlatest
     - python: "3.8"
       env: TOXENV=py38-pytestmaster
-    - python: "3.8"
-      env: TOXENV=py38-pytestfeatures
 
     - stage: deploy
       python: '3.8'

tox.ini

@@ -2,15 +2,14 @@
 envlist=
   linting
   py{27,34,35,36,37,38}-pytestlatest
-  py38-pytest{master,features}
+  py38-pytestmaster
 
 [testenv]
 passenv = USER USERNAME
 extras = testing
 deps =
   pytestlatest: pytest
   pytestmaster: git+https://github.com/pytest-dev/pytest.git@master
-  pytestfeatures: git+https://github.com/pytest-dev/pytest.git@features
 commands=
   pytest {posargs}