ci: general pip cleanup

Cleanup all pip commands in the various workflow
- drop the install/upgrade for setuptool pip and wheel, seems like this
  was introduced few years back to work around some old bug and it's not
  needed anymore
- use pip instead of pip3, that's probably been equivalent for quite a
  long time in the CI image

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>