First, SHAME ON YOU for providing an easy destructive install! It's inexcusable. This should not be an option at all. Your instructions for removal didn't entirely work on MacOS 10.13.6 (High Sierra), probably because High Sierra reformats the hard drive. Here's what DOES work:
1. Select the merged calendar and Search for "hebcal" and delete. (On High Sierra, this removed very little.)
2. Delete remaining items using successive searches that capture multiple items—e.g., month names (Iyyar, Adar, Sh'vat, etc.) and other items (Omer). In a short time, you can clean up the calendar.
P.S. I've been a UX Designer for many years. Allowing a destructive install breaks a primary rule for good behavior. The fact that the calendar is free just means that you provide no support. Shame! At least update your removal instructions to include this workaround
Customer support service by UserEcho