id_sysfs: simplify without ktype, remove release

A ktype is good to use when there are many kobjects that behave the
same.  But id_sysfs has only one and there is no need for similar types.
Simplify by removing ktype and using __ATTR.

The sysfs documentation (Documentation/kobject.txt) says a release
method must be used.  But the example they refer to doesn't
(samples/kobject/kobject-example.c).  Remove the release function.