* inferior.h (context_switch_to): Delete.
* infrun.c (context_switch): Don't save and load infrun state.
(context_switch_to): Delete.
* infcmd.c (proceed_thread_callback): Replace context_switch_to
calls by switch_to_thread calls.
* gdbthread.h (save_infrun_state, load_infrun_state): Delete.
* thread.c (main_thread_state, main_thread_executing): Delete.
(inferior_thread): Delete references to them.
(add_thread_silent): Fix case where we're adding a thread with the
same ptid as an exited thread. Remove references to
context-switching.
(load_infrun_state, save_infrun_state): Delete.
(thread_alive, is_thread_state, any_running, is_executing)
(set_executing): Remove the special handling for targets that
don't register any thread.
(restore_current_thread, thread_apply_all_command)
(do_captured_thread_select): Unconditionally call
switch_to_thread.
* mi/mi-main.c (mi_cmd_execute): Check for exited threads.
Call switch_to_thread instead of context_switch_to.