Don't show headers for empty sections

[difosfor]

Per example at: https://tsdocs.dev/docs/@liveryvideo/player/7.9.0-beta.4/classes/LiveryPlayer.html deselect the Inherited member visibility and then scroll down to see empty sections for Methods - attributes, Methods - controllers, etc. I think these are derived from usage of @group in the tsdoc of the LitElement from the lit package that is extended here. These sections do have members while Inherited members are enabled, but after that is disabled they are empty.