ffmpeg: disable Centipede again (google#12290)

It is not stable, there are multiple bus errors:

Step google#22 - "build-check-centipede-none-x86_64":
/usr/local/bin/run_fuzzer: line 227: 172132 Bus error (core dumped) bash
-c "$CMD_LINE"

Disable it for now, to let other recent changes take effect, we can
revisit it later.

Fixes: 0318a94

projects/ffmpeg/project.yaml

@@ -14,7 +14,6 @@ auto_ccs:
  - "[email protected]"
 fuzzing_engines:
  - afl
- - centipede
  - honggfuzz
  - libfuzzer
 sanitizers: