Remove undefined functions.
Remove unused function add_long_to_buf.
Remove unused function handle_drop.
Remove unused function get_shape_idx.
Remove unused function re_lookbehind.
Remove unused function highlight_gui_color_rgb.
Remove unused function ui_inchar_undo.
Remove undefined function suspend_shell.
Remove unused function vim_free_in_input_buf.
Remove unused function push_raw_key.
Remove unused function yank_cut_buffer0.
Remove undefined function gui_show_popupmenu + call.
Remove undefined function gui_show_popupmenu + its unused return defines.
Remove unused function unset_global_local_option.
Remove undefined function server_to_input_buf.
Remove unused function free_register.
Remove undefined function adjust_clip_reg.
Remove unused function is_autocmd_blocked.
Remove unused function get_fpos_of_mouse.
Remove undefined function clip_yank_selection.