Remove useless cover target

This repository contains code for testing and we have no real benefit
with code coverage.

Change-Id: I3253f8f5a679f68868e1b9f3200ed8f65eff7ab6
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

test-requirements.txt

@@ -1,2 +1 @@
 stestr>=1.0.0 # Apache-2.0
-coverage>=4.0 # Apache-2.0

tox.ini

@@ -21,16 +21,6 @@ commands = pre-commit run --all-files --show-diff-on-failure {posargs}
 [testenv:venv]
 commands = {posargs}
 
-[testenv:cover]
-setenv =
-    {[testenv]setenv}
-    PYTHON=coverage run --source ironic_tempest_plugin --parallel-mode
-commands =
-    stestr run {posargs}
-    coverage combine
-    coverage html -d cover
-    coverage xml -o cover/coverage.xml
-
 [testenv:docs]
 deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/doc/requirements.txt