Nuke the tox packaging job (#12334)

.github/workflows/tests.yml

@@ -27,7 +27,6 @@ jobs:
           - "check_codestyle"
           - "check_isort"
           - "mypy"
-          - "packaging"
 
     steps:
       - uses: actions/checkout@v2

changelog.d/12334.misc

@@ -0,0 +1 @@
+Remove the `tox` packaging job: it will be redundant once #11537 lands.

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = packaging, py37, py38, py39, py310, check_codestyle, check_isort
+envlist = py37, py38, py39, py310, check_codestyle, check_isort
 
 # we require tox>=2.3.2 for the fix to https://github.com/tox-dev/tox/issues/208
 minversion = 2.3.2
@@ -138,14 +138,6 @@ setenv =
 commands =
     python -m synmark {posargs:}
 
-[testenv:packaging]
-skip_install = true
-usedevelop = false
-deps =
-    check-manifest
-commands =
-    check-manifest
-
 [testenv:check_codestyle]
 extras = lint
 commands =