Remove no-longer-used cursor_in_echo_area code

Remove no-longer-used cursor_in_echo_area code

* dispnew.c (set_window_cursor_after_update, update_frame_1):
Remove checks for negative cursor_in_echo_area, since this var is
a boolean, and has been a boolean for some time.  Simplify.
* dispnew.c (init_display):
* xdisp.c (message3_nolog, vmessage): Use bool for boolean.