compat.h: drop COMPAT_HANDLE_PARAM()

compat.h: drop COMPAT_HANDLE_PARAM()

The need for 8844ed299a ("x86/dmop: Fix compat_dm_op() ABI") has made
clear that its presence is actively dangerous. At the hypercall entry
points XEN_GUEST_HANDLE_PARAM() should be used anyway (regardless of
whether these are native or compat entry points), and passing around
handles internally shouldn't use their compat representation either.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>