Remove LIBRARIES arg from w32_delayed_load and friends.

Remove LIBRARIES arg from w32_delayed_load and friends.
These always use Vdynamic_library_alist anyway.

* src/image.c (Finit_image_library, lookup_image_type)
(define_image_type): Remove now-unneeded second arg.
(init_xpm_functions, init_png_functions, init_jpeg_functions)
(init_tiff_functions, init_gif_functions, init_svg_functions):
Arglist and w32_delayed_load calling convention changed.
(gs_type): Remove init_gs_functions; there is no such function.

* src/gnutls.c (init_gnutls_functions): Caller changed; remove arg.
(Fgnutls_available_p): Caller changed.

* src/xml.c (init_libxml2_functions, Flibxml_parse_html_region)
(Flibxml_parse_xml_region): Likewise.

* src/dispextern.h (struct image_type): Remove arg from init function.

* src/w32.c (w32_delayed_load): Remove LIBRARIES argument; always use
Vdynamic_library_alist.

* lisp/image.el (image-type-available-p): Change caller to
init-image-library.