nir_lower_mediump: Drop assertion about not containing movs.

A 1D texture operation may need to do a mov to turn a reference to a
channel of an SSA value into a scalar value to be passed as the texture
coordinate (since texture srcs can't do swizzles).  Seen in
amnesia-the-dark-descent/low/46.shader_test() for example, where a 1D
texture is used to remap each of r,g,b from a previous texture result.

Besides, the nir_op_is_vec() case will (perhaps surprisingly) look through
a mov, anyway.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16616>

src/compiler/nir/nir_lower_mediump.c

@@ -465,12 +465,6 @@ nir_fold_16bit_sampler_conversions(nir_shader *nir,
 
             nir_alu_type src_type = nir_tex_instr_src_type(tex, i);
 
-            if (src_alu->op == nir_op_mov) {
-               assert(!"The IR shouldn't contain any movs to make this pass"
-                       " effective.");
-               continue;
-            }
-
             /* Handle vector sources that are made of scalar instructions. */
             if (nir_op_is_vec(src_alu->op)) {
                /* See if the vector is made of f16->f32 opcodes. */