[extensions] Remove an obsolete TODO in ChromeExtensionsAPIClient

ChromeExtensionsAPIClient::ShouldHideResponseHeader() allows to hide the
Dice response header from extension. As opposed to the TODO comment,
this code is still needed because the response header may be attached to
a regular renderer-initiated navigation.

Bug: 890006
Change-Id: I6eb8bd880c4354b604fd0c1f9fd152c332ffd3bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2148319
Auto-Submit: Alex Ilin <alexilin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Alex Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759208}

chrome/browser/extensions/api/chrome_extensions_api_client.cc

@@ -127,9 +127,6 @@ bool ChromeExtensionsAPIClient::ShouldHideResponseHeader(
     const std::string& header_name) const {
   // Gaia may send a OAUth2 authorization code in the Dice response header,
   // which could allow an extension to generate a refresh token for the account.
-  // TODO(crbug.com/890006): Determine if the code here can be cleaned up
-  // since browser initiated non-navigation requests are now hidden from
-  // extensions.
   return (
       (url.host_piece() == GaiaUrls::GetInstance()->gaia_url().host_piece()) &&
       (base::CompareCaseInsensitiveASCII(header_name,