libxc: remove superpages option for pv domains

libxc: remove superpages option for pv domains

The pv domain builder currently supports the additional flag
"superpages" to build a pv domain with 2MB pages. This feature isn't
being used by any component other than the python xc bindings.

Remove the flag and its support from the xc bindings and the domain
builder

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>