Update update_playground.sh
Update update_playground.sh

 - Remove unused androidx-plugin updates
 - Provide switch for update_playground.sh to only update snapshot id

Test: ./development/update_playground.sh
Change-Id: I957c6eaae6f4740a1ec8b20fe3570007551ccac6

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