[Flags] Remove obsolete --extra-masking flag

Change-Id: I668a4ac9ce80daa1952b05fdee754db190f3fb3c
Reviewed-on: https://chromium-review.googlesource.com/853866Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50408}

src/flag-definitions.h

@@ -465,8 +465,6 @@ DEFINE_BOOL(turbo_store_elimination, true,
 DEFINE_BOOL(trace_store_elimination, false, "trace store elimination")
 DEFINE_BOOL(turbo_rewrite_far_jumps, true,
             "rewrite far to near jumps (ia32,x64)")
-// TODO(rmcilroy): Remove extra_masking once the finch experiment is removed.
-DEFINE_BOOL(extra_masking, false, "obsolete - has no effect")
 
 #ifdef DISABLE_UNTRUSTED_CODE_MITIGATIONS
 #define V8_DEFAULT_UNTRUSTED_CODE_MITIGATIONS false