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