Take your duplicate Google Calendar events and merge them into one event.
This Chrome extension also uses the user defined colors of each calendar to create a beautiful gradient for each event.
After installed, click on the plugin to activate then refresh Google Calendar to see your new cleaned up Google Calendar.
Modified from: https://chrome.google.com/webstore/detail/event-merge-for-google-ca/idehaflielbgpaokehlhidbjlehlfcep
Repo at: https://github.com/karjna/gradient-gcal-event-merge