feat(popoverTriggerDirective): remove custom popover trigger events

This option is just bloat and a distraction right now. In the near term, this
can easily be implemented by consumers of the directive. In the long term, we
can easily add this option back if there is a clear need.
feat(popoverTriggerDirective): simply trigger interface

Only allow the re-popover-trigger directive as an attribute. Allowing many
different usages of rs-popover-trigger caused unnecessary bloat to the
interface.