Stop to use $SPHINX_TEST_TEMPDIR envvar

At once, we added $SPHINX_TEST_TEMPDIR to keep intermediate files of
testing to investigate the failures.  At present, we've used pytest
as a test runner.  And it keeps temporary directories of last 3
testings.  So this starts to use it instead of $SPHINX_TEST_TEMPDIR.
https://docs.pytest.org/en/latest/tmpdir.html#the-default-base-temporary-directory

1 files changed, 0 insertions, 1 deletions

diff --git a/tox.ini b/tox.ini
index 20f8cfdc8..13e6f6be3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,7 +18,6 @@ extras =
     websupport
 setenv =
     PYTHONWARNINGS = all,ignore::ImportWarning:pkgutil,ignore::ImportWarning:importlib._bootstrap,ignore::ImportWarning:importlib._bootstrap_external,ignore::ImportWarning:pytest_cov.plugin,ignore::DeprecationWarning:site,ignore::DeprecationWarning:_pytest.assertion.rewrite,ignore::DeprecationWarning:_pytest.fixtures,ignore::DeprecationWarning:distutils
-    SPHINX_TEST_TEMPDIR = {envdir}/testbuild
 commands=
     pytest --durations 25 {posargs}