Remove undefined upstream environment from tox.ini

Commit number 3fa3be7edef356fe42ed3c6adc21590604634665 initially
added the upstream testenv, but it was merged to the 'projects'
testenv a long time ago. Which is now obsolete, because of the
split to project-config.

Change-Id: I2d011af7df2ad9d14d2db67fa78c4dc6e4e4cbb6
Merge "Remove undefined upstream environment from tox.ini"