As Dawiese noted:
dawieseDec 24, 2016 12:38 PM in response to picas
Level 1 (4 points)
Dec 24, 2016 12:38 PM in response to picas
"Please note: The Delete button does not exist for "Other" calendars in iOS 10. Apple developers have overlooked this. "
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It's one of hundreds of small irritations, glitches, etc. that need fixing in the iOS and Mac Os.
Seeing something that says "Subscribed" without any way of "Unsubscribing" is illogical. In this era, it's also unnerving as it seems as if a 3rd party has taken control of the iOS device.
On the Mac, it even had a WiFi signal next to it! Fortunately, control-clicking that one does permit deletion (or was it unchecking that worked?). Seems there is no easy way of getting it back even if one wanted to! (I was hoping to test which method vanquished it!)