(Fw32_registered_hot_keys): Don't return the nil values corresponding

(Fw32_registered_hot_keys): Don't return the nil values corresponding
to deleted entries; they are an implementation detail.
(gray_bitmap_width, gray_bitmap_height, gray_bitmap_bits): Remove variables.
(w32_pass_extra_mouse_buttons_to_system, w32_strict_fontnames,
w32_pass_multimedia_buttons_to_system, w32_strict_painting,
Vw32_charset_info_alist, w32_to_x_color, w32_init_class, w32_createscrollbar,
w32_createwindow, my_post_msg, w32_get_modifiers, w32_grabbed_keys,
cancel_all_deferred_msgs): Make static.
(syms_of_w32fns) <w32-pass-multimedia-buttons-to-system>: Fix typo in docstring.