@utils.service_type was introduced with 'Initial split from
python-novaclient' commit and used for CLI. Now both Python and
Command-line APIs for each version work well without this decorator.
Unused 'get_service_type' function is removed too.
'utils.retype_method' removed as well because everything works well
without it.
Change-Id: Ic2470d8ca9d581b7c47da8d7e6a414c3c78ad27a
Partial-Bug: #1643584
Related-Bug: #1621126