xlib_libX11: removed redundant HOST_FOO_DEPENDENCIES and incorrect target dependency

By deriving HOST_XLIB_LIBX11_DEPENDENCIES from XLIB_LIBX11_DEPENDENCIES, it
turned out that that one had a redundant dependency on xproto_bigreqsproto.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>