Now that all the build scripts are compatible with both Python 2 and 3,
we can flip the switch and tell Meson to use the latter.
Since Meson already depends on Python 3 anyway, this means we don't need
two different Python stacks to build Mesa.
Signed-off-by: Mathieu Bridon <firstname.lastname@example.org>
Reviewed-by: Eric Engestrom <email@example.com>
Reviewed-by: Dylan Baker <firstname.lastname@example.org>