libxl: Remove/deprecate libxl_get_required_*_memory from the API

libxl: Remove/deprecate libxl_get_required_*_memory from the API

These are now redundant because shadow_memkb and iommu_memkb are now
defaulted automatically by libxl_domain_need_memory and
libxl_domain_create etc.  Callers should not now call these; instead,
they should just let libxl take care of it.

libxl_get_required_shadow_memory was introduced in f89f555827a6
  "remove late (on-demand) construction of IOMMU page tables"
We can freely remove it because it was never in any release.

libxl_get_required_shadow_memory has been in libxl approximately
forever.  It should probably not have survived the creation of
libxl_domain_create, but it seems the API awkwardnesses we see in
recent commits prevented this.  So we have to keep it.  It remains
functional but we can deprecate it.  Hopefully we can get rid of it
completely before we find the need to change the calculation to use
additional information which its arguments do not currently supply.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>