ra: Delete the conflict lists in ra_set_finalize

They are never used after the set is finalized so there's no reason to keep
them around.

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/util/register_allocate.c

          }
       }
    }
+
+   for (b = 0; b < regs->count; b++) {
+      ralloc_free(regs->regs[b].conflict_list);
+      regs->regs[b].conflict_list = NULL;
+   }
 }
 
 static void