Remove use of old API doc methods

Remove use of old API doc methods

The following deprecated methods, intended for overriding by extensions,
are no longer called and are hard deprecated.

* ApiBase::getDescription() (deprecated in 1.25)
* ApiBase::getParamDescription() (deprecated in 1.25)
* ApiBase::getExamples() (deprecated in 1.25)
* ApiBase::getDescriptionMessage() (deprecated in 1.30)

Also, the 'APIGetDescription' and 'APIGetParamDescription' hooks have
been removed, as their only use was to allow extensions to override
values returned by getDescription() and getParamDescription(),
respectively.

Change-Id: I486c4ccab4eca6a85cb17c30dbb2439876123ba1