ci: turn off FuzzBuzz

I don't think anyone uses it.

src/fuzz/fuzz.h

@@ -6,6 +6,3 @@
 
 /* The entry point into the fuzzer */
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
-
-/* https://docs.fuzzbuzz.io/developer-documentation/porting-targets-to-fuzzbuzz/libfuzzer-targets */
-int FuzzerEntrypoint(const uint8_t *data, size_t size);