[libFuzzer] Docs: delete occurrences of max_len in libfuzzer_options.

Otherwise, the readers might get an idea to use max_len in there, which
is deprecated and discouraged now.

Bug: 539572
Change-Id: I6a2d14ca59326fb4e037caec30e05d731f608520
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611872
Commit-Queue: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Abhishek Arya <inferno@chromium.org>
Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Auto-Submit: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659938}

testing/libfuzzer/efficient_fuzzer.md

@@ -271,8 +271,8 @@ definition in BUILD.gn file:
 fuzzer_test("my_fuzzer") {
   ...
   libfuzzer_options = [
-    "max_len=2048",
-    "len_control=0",
+    # Suppress stderr output (not recommended, as it may silence useful info).
+    "close_fd_mask=2",
   ]
 }
 ```

testing/libfuzzer/fuzzer_test.gni

@@ -19,7 +19,7 @@ import("//testing/test.gni")
 # - environment_variables - certain whitelisted environment variables for the
 # - configs_to_remove - (EXPERIMENTAL, don't use) configs to remove.
 # fuzzer (AFL_DRIVER_DONT_DEFER is the only one allowed currently).
-# - libfuzzer_options - options for the fuzzer (e.g. -max_len=N or -timeout=N).
+# - libfuzzer_options - options for the fuzzer (e.g. -close_fd_mask=N).
 # - asan_options - AddressSanitizer options (e.g. allow_user_segv_handler=1).
 # - msan_options - MemorySanitizer options.
 # - ubsan_options - UndefinedBehaviorSanitizer options.

testing/libfuzzer/reference.md

@@ -182,8 +182,8 @@ To specify these options for ClusterFuzz, list all parameters in
 fuzzer_test("my_fuzzer") {
   ...
   libfuzzer_options = [
-    "max_len=2048",
-    "use_traces=1",
+    # Suppress stdout and stderr output (not recommended, as it may silence useful info).
+    "close_fd_mask=3",
   ]
 }
 ```