libxc: remove most of tools/libxc/xc_dom_compat_linux.c

libxc: remove most of tools/libxc/xc_dom_compat_linux.c

In tools/libxc/xc_dom_compat_linux.c xc_linux_build() is the only
domain building function used by an in-tree component (qemu-xen) which
is really necessary.

Remove the other domain building functions and the unused python
wrapper xc.linux_build() referencing one of the to be removed
functions.

Suggested-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>