py, unix: Allow to compile with -Wunused-parameter.

See issue #699.

py/objslice.c

@@ -39,6 +39,8 @@ typedef struct _mp_obj_ellipsis_t {
 } mp_obj_ellipsis_t;
 
 STATIC void ellipsis_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t self_in, mp_print_kind_t kind) {
+    (void)self_in;
+    (void)kind;
     print(env, "Ellipsis");
 }
 
@@ -65,6 +67,7 @@ typedef struct _mp_obj_slice_t {
 } mp_obj_slice_t;
 
 STATIC void slice_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind) {
+    (void)kind;
     mp_obj_slice_t *o = o_in;
     print(env, "slice(");
     mp_obj_print_helper(print, env, o->start, PRINT_REPR);