i965: Drop assert about number of uniforms in ARB handling.

i965: Drop assert about number of uniforms in ARB handling.

My recent prog_to_nir patch started making new sampler uniforms, which
apparently increased the number of parameters.  We used to poke at the
one parameter directly, making it important that there was only one,
but we haven't done that in a while.  It should be safe to just delete
the assertion.

Fixes: 1c0f92d8a8c "nir: Create sampler variables in prog_to_nir."
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>