Rely on use_fuzzing_engine && optimize_for_fuzzing to define WEBRTC_UNSAFE_FUZZER_MODE.

Depends on https://chromium-review.googlesource.com/c/chromium/src/+/1074830.

Bug: chromium:847106, chromium:646404, chromium:844647
Change-Id: I401d518646e032e24989d343c00c307563e23ddf
Reviewed-on: https://webrtc-review.googlesource.com/79187
Commit-Queue: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23438}
diff --git a/BUILD.gn b/BUILD.gn
index 532fe54..3790e4a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -312,7 +312,7 @@
     ]
   }
 
-  if (use_libfuzzer || use_drfuzz || use_afl) {
+  if (use_fuzzing_engine && optimize_for_fuzzing) {
     # Used in Chromium's overrides to disable logging
     defines += [ "WEBRTC_UNSAFE_FUZZER_MODE" ]
   }