st/nine: Remove useless optimisations to avoid constant uploads

Previous removed path to upload constants was trying to do as
few uploads as possible.
The path kept doesn't benefit these optimisations, thus remove them.

Signed-off-by: Axel Davy <axel.davy@ens.fr>
st/nine: fix the size of the constant buffer with relative addressing

When relative addressing is on, we have to copy the constants defined in the
shader in the constant file.
The size for the new constant buffer was incorrectly calculated.

Signed-off-by: Axel Davy <axel.davy@ens.fr>