Drop install_command usage in tox

Use the default value provided by tox:

https://tox.readthedocs.io/en/latest/config.html#conf-install_command

See discussion on the openstack-discuss ML [1]
for the complete context.

[1] http://lists.openstack.org/pipermail/openstack-discuss/2020-April/014237.html

Change-Id: I93c60668c9510f4479d268aab69d0117a53b2c01
Signed-off-by: Goutham Pacha Ravi <gouthampravi@gmail.com>
1 file changed