tox: remove no longer needed pip download=True

Whatever pip is used almost certainly has the new resolver by now.

Author: bluetech

tox.ini

@@ -173,9 +173,6 @@ description =
     run reverse dependency testing against pytest plugins under `{basepython}`
 # use latest versions of all plugins, including pre-releases
 pip_pre=true
-# use latest pip to get new dependency resolver (#7783)
-download=true
-install_command=python -m pip install {opts} {packages}
 changedir = testing/plugins_integration
 deps = -rtesting/plugins_integration/requirements.txt
 setenv =