Although it's convenient to inherit from TimeNodeContext, but only
mpNode is used so it's really not necessary.

Change-Id: I922774df4c420ee9982f1c31e720f4fd85991e02
Reviewed-on: https://gerrit.libreoffice.org/57395
Tested-by: Jenkins
Reviewed-by: Mark Hung <marklh9@gmail.com>