Remove mylyn dependency

mylyn has been removed from simrel in 2022-06 and some workaround in the simrel have been removed. see https://git.eclipse.org/r/c/simrel/org.eclipse.simrel.build/+/189614/4 and according bugzilla for reference. (https://bugs.eclipse.org/bugs/show_bug.cgi?id=569078) 

Mylyn asked a while to be removed from simrel, and also annouced that there will be more more releases (https://www.eclipse.org/lists/cross-project-issues-dev/msg18358.html) on May, 2021, but mylyn stayed because of dependent projects ( for example egit )

due to orbit changes also targeted for 2022-06, the necessary dependencies are also removed. we should remove our dependency to mylyn, and migrate notification and discovery.