Clean up Gradle dependencies for v7 demo app
Clean up Gradle dependencies for v7 demo app

Test: ./gradlew :support-v7-demos:assembleDebug and run the demo
Change-Id: Iee069a85f9fd739e2e5251805c6d20851d905997

androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx