remove state from view callback and sst methods

[temeo]

There are completely unused state/state_len parameters in

• wsrep_view_cb_t
• wsrep_sst_donate_cb_t
• sst_received

These unused parameters should be removed as there is no intended use for them now or in the future.

[denis-protivensky]

One more likely unused candidate: wsrep_init_args::state variable.