agx: drop scratch regs for spilling

remnant of an old approach.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28483>

src/asahi/compiler/agx_register_allocate.c

@@ -1381,12 +1381,6 @@ agx_ra(agx_context *ctx)
    unsigned reg_file_alignment = MAX2(max_ncomps, 8);
    assert(util_is_power_of_two_nonzero(reg_file_alignment));
 
-   if (spilling) {
-      /* We need to allocate scratch registers for lowering spilling later */
-      effective_demand = MAX2(effective_demand, 6 * 2 /* preloading */);
-      effective_demand += reg_file_alignment;
-   }
-
    unsigned demand = ALIGN_POT(effective_demand, reg_file_alignment);
    assert(demand <= max_possible_regs && "Invariant");