build: Remove last leftover -enable-dse-memoryssa=false flag

These flags were removed in crrev.com/824947 but the win
thinlto flag was accidentally left behind.

Bug: 1127713
Change-Id: Ie7698e4a5819eb2dcd97effcf3715f208f75801f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637577
Commit-Queue: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Hans Wennborg <hans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844795}

build/config/compiler/BUILD.gn

@@ -652,9 +652,6 @@ config("compiler") {
         "-Wl,--thinlto-cache-policy,$cache_policy",
       ]
 
-      # TODO(https://crbug.com/1127713): Investigate, remove.
-      ldflags += [ "-Wl,-mllvm,-enable-dse-memoryssa=false" ]
-
       ldflags += [ "-Wl,--lto-O" + lto_opt_level ]
       if (thin_lto_enable_optimizations) {
         # TODO(gbiv): We ideally shouldn't need to specify this; ThinLTO