CA-141955: Use new search path feature from xcp-idl

Now we can specify a search path in xenopsd.conf we no longer need to hardcode
all the paths to the binaries we need. Some are still needed where the basename
differs from what is expected but many can disappear.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
I think Jon wanted to avoid introducing /usr/bin to the search path if possible.   Maybe keep the eliloader and pygrub paths and drop /usr/bin here?