doc: fix unused warning
doc: fix unused warning

Fix gtk-doc warning by ignoring the new private header.

./spice-gtk-unused.txt:1: warning: 12 unused declarations.They should be
added to spice-gtk-sections.txt in the appropriate place.

While at it, fix grabsequence header incorrect file name.

Signed-off-by: Marc-André Lureau <a6f2b960a4aca61381fc650a67901b2ac8e83e6d@redhat.com>

fgouget/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk