Clean up various bits of Haiku code

Clean up various bits of Haiku code

* src/haiku_font_support.cc (BFont_string_width): Delete unused
function.
* src/haiku_support.cc (BWindow_new): Clean up type of `view'.
(BWindow_quit): Clean up coding style.
(BView_mouse_down, BView_mouse_up, BView_mouse_moved): Delete
unused functions.
(unwind_popup_file_dialog): Clean up coding style.
(be_popup_file_dialog_safe_set_target): Delete function.
(be_popup_file_dialog): Improve code clarity.
* src/haiku_support.h: Fix coding style.
* src/haikufns.c (haiku_get_color, haiku_display_info_for_name)
(check_haiku_display_info, Fhaiku_read_file_name)
(Fx_display_save_under, Fhaiku_frame_restack): Remove references
to "Be displays" and replace them with "Haiku displays".
* src/haikuselect.h: Clean up coding style.
* src/haikuterm.c (haiku_read_socket): Clean up coding style and
fix a few latent bugs.