Remove token unregistration on shutdown

This was functionally incorrect (unregistering the wrong tokens) and
is causing crashes in M83, blocking the WebProtect release. Since it
was only added to support privacy requirements for APP scanning,
simply remove this functionality and I'll correctly re-introduce it
in M84.

Bug: 1068732
Change-Id: I38ac3ba3a39564f1342c3cb4f9f57794bf2aeace
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144467Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758324}

chrome/browser/safe_browsing/cloud_content_scanning/binary_fcm_service.cc

@@ -74,10 +74,6 @@ BinaryFCMService::BinaryFCMService()
 BinaryFCMService::~BinaryFCMService() {
   if (gcm_driver_ != nullptr)
     gcm_driver_->RemoveAppHandler(kBinaryFCMServiceAppId);
-  for (const auto& token_to_callback : message_token_map_) {
-    const std::string& token = token_to_callback.first;
-    UnregisterInstanceID(token, base::DoNothing());
-  }
 }
 
 void BinaryFCMService::GetInstanceID(GetInstanceIDCallback callback) {