Kill the return value for all MI command functions.

	Kill the return value for all MI command functions.
	* mi/mi-cmds.h (enum mi_cmd_result): Remove.
	(mi_cmd_argv_ftype): Change return type to void.

	* mi/mi-main.c: Adjust all function that implement
	MI commands to return nothing.
	(struct captured_mi_execute_command_actions):
	Remove the rc field.
	(mi_cmd_execute): Return nothing.
	(mi_execute_async_cli_command): Return nothing.
	(mi_cmd_exec_interrupt): Don't print ^done here.
	(mi_cmd_target_select): Don't print ^connected here.
	(captured_mi_execute_command): Don't check for MI_CMD_DONE.
	Special-case -target-select and output ^connected, not ^done.

	* mi/mi-cmd-break.c: Adjust.
	* mi/mi-cmd-disas.c: Adjust.
	* mi/mi-cmd-env.c: Adjust.
	* mi/mi-cmd-file.c: Adjust.
	* mi/mi-cmd-stack.c: Adjust.
	* mi/mi-cmd-target.c: Adjust.
	* mi/mi-cmd-var.c: Adjust.
	* mi/mi-interp.c: Adjust.
	* mi/mi-symbol-cmds.c: Adjust.