Remove duplicated policy deprecation messge

DeveloperToolsDisabled policy is marked as deprecated in policy_templates
and DeveloperToolsPolicyHandler. Remove the one in handler so that the
deprecation message only appears once.

Bug: 902603
Change-Id: Ia9a78cd4667eb39b5ec3e82399fcd44ae1556de1
Reviewed-on: https://chromium-review.googlesource.com/c/1326843Reviewed-by: Pavol Marko <pmarko@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607241}

chrome/browser/policy/developer_tools_policy_handler.cc

@@ -40,10 +40,6 @@ PolicyCheckResult CheckDeveloperToolsDisabled(
   if (!developer_tools_disabled)
     return PolicyCheckResult::kNotSet;
 
-  if (errors) {
-    errors->AddError(key::kDeveloperToolsDisabled, IDS_POLICY_DEPRECATED);
-  }
-
   if (!developer_tools_disabled->is_bool()) {
     if (errors) {
       errors->AddError(key::kDeveloperToolsDisabled, IDS_POLICY_TYPE_ERROR,