amd64: Remove write-only variable start_callee_saves_offset.

ir/be/amd64/amd64_transform.c

@@ -41,7 +41,6 @@ static ir_mode         *mode_flags;
 static amd64_cconv_t   *current_cconv = NULL;
 static be_start_info_t  start_mem;
 static be_start_info_t  start_val[N_AMD64_REGISTERS];
-static size_t           start_callee_saves_offset;
 static size_t           start_params_offset;
 static pmap            *node_to_stack;
 static be_stackorder_t *stackorder;
@@ -1397,7 +1396,6 @@ static ir_node *gen_Start(ir_node *node)
 	}
 
 	/* callee saves */
-	start_callee_saves_offset = o;
 	for (size_t i = 0; i < N_AMD64_REGISTERS; ++i) {
 		if (!rbitset_is_set(cconv->callee_saves, i))
 			continue;