chore: remove patrons.json

refs:
- aea6659d0b
- https://info.firefish.dev/notes/9s1n283sb10rh869

Now that the domain name joinfirefish[dot]org is expired,
there is no Firefish server that reads this file.

v20240206-v20240210 refers to the old forge URL,
v20240212-v20240405 reads the local `patrons.json`,
and `/api/patrons` endpoint was removed in v20240413.

patrons.json

@@ -1,4 +0,0 @@
-{
-  "patrons": [],
-  "sponsors": []
-}