xkeyboard-config: disable 'runtime deps as build time deps'

Fixes http://autobuild.buildroot.net/results/f11/f11687ae661f9d3570c55a9d62a7822e667ad9ad/



xkeyboard-config has runtime dependencies (when using X11) on xproto and
libX11, and by default checks at build time if they are available.

Disable this check as it doesn't apply for wayland and the needed deps are
taken care of by BR for X11.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>