[main] do not set state->keyboard twice

state->keyboard is set already in set_keyboard, there is no need to do
the work twice.

src/main.c

@@ -1290,7 +1290,6 @@ add_display_and_keyboard_for_terminal (state_t    *state,
   display = ply_text_display_new (state->terminal);
 
   ply_list_append_data (state->text_displays, display);
-  state->keyboard = keyboard;
   set_keyboard (state, keyboard);
 }