v3d: do not report alpha-test as supported

This triggers lowering in the state-tracker, which makes things a bit
simpler.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/broadcom/compiler/nir_to_vir.c

@@ -2027,11 +2027,6 @@ ntq_emit_intrinsic(struct v3d_compile *c, nir_intrinsic_instr *instr)
                                vir_uniform(c, QUNIFORM_VIEWPORT_Z_OFFSET, 0));
                 break;
 
-        case nir_intrinsic_load_alpha_ref_float:
-                ntq_store_dest(c, &instr->dest, 0,
-                               vir_uniform(c, QUNIFORM_ALPHA_REF, 0));
-                break;
-
         case nir_intrinsic_load_sample_mask_in:
                 ntq_store_dest(c, &instr->dest, 0, vir_MSF(c));
                 break;