tools: update link of `ICU data slicer`
unicode-org/icu repo has renamed its default branch to main also, this pr update the link to unicode-org/icu old master branch.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
unicode-org/icu repo has renamed its default branch to main also, this pr update the link to unicode-org/icu old master branch.