website: Remove reference to python3-six in the building gem5 doc

https://gem5-review.googlesource.com/c/public/gem5/+/57969

Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Change-Id: If2c7c92809a2194df630c0f6044ebf44ff5f30b6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/57930
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
1 file changed