gdk/win32: fix defined but not used warnings

gdk/win32: fix defined but not used warnings

[30/1038] Compiling C object gdk/win32/libgdk-win32.a.p/gdkmain-win32.c.obj
../gdk/win32/gdkmain-win32.c:146:1: warning: 'gdk_win32_finalize_ole' defined but not used [-Wunused-function]
  146 | gdk_win32_finalize_ole (void)
      | ^~~~~~~~~~~~~~~~~~~~~~
../gdk/win32/gdkmain-win32.c:113:1: warning: 'gdk_win32_finalize_com' defined but not used [-Wunused-function]
  113 | gdk_win32_finalize_com (void)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>