[webrtc] Remove use_afl GN arg

Bug: chromium:492241998
Change-Id: Iaba8884cfa4a620ba110195847f3b4026a6a6964
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/459522
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Auto-Submit: Jon Toohill <jtoohill@google.com>
Cr-Commit-Position: refs/heads/main@{#47354}

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 06421da..cf54ae0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -603,7 +603,7 @@
   }
 }
 
-if (use_libfuzzer || use_afl) {
+if (use_libfuzzer) {
   # This target is only here for gn to discover fuzzer build targets under
   # webrtc/test/fuzzers/.
   group("webrtc_fuzzers_dummy") {