Revert "Send platform_version to Gaia for Dent auth flow"

This reverts commit e81b8956.

Reason for revert: http://b/123630392#comment55

Original change's description:
> Send platform_version to Gaia for Dent auth flow
> 
> Send missing parameter |platform_version| to Gaia during Chrome OS
> add account flow.
> 
> Bug: 1064677
> Change-Id: I6e4745eb62fdc34c3ed303d138639e6d26bdb81e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2121264
> Commit-Queue: Andrei Salavei <solovey@google.com>
> Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
> Reviewed-by: Kush Sinha <sinhak@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#755366}

TBR=xiyuan@chromium.org,sinhak@chromium.org,solovey@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1064677
Change-Id: I69eeda6d00241e4c7ccfbaa7c96b6defee73f316
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153054Reviewed-by: Kush Sinha <sinhak@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760094}

chrome/browser/resources/gaia_auth_host/authenticator.js

@@ -55,7 +55,6 @@ cr.define('cr.login', function() {
    *   isLoginPrimaryAccount: boolean,
    *   email: string,
    *   constrained: string,
-   *   platformVersion: string,
    *   readOnlyEmail: boolean,
    *   service: string,
    *   dontResizeNonEmbeddedPages: boolean,

chrome/browser/ui/webui/signin/inline_login_handler_chromeos.cc

@@ -21,7 +21,6 @@
 #include "chromeos/components/account_manager/account_manager.h"
 #include "chromeos/components/account_manager/account_manager_factory.h"
 #include "chromeos/constants/chromeos_features.h"
-#include "chromeos/dbus/util/version_loader.h"
 #include "components/signin/public/identity_manager/account_info.h"
 #include "components/signin/public/identity_manager/identity_manager.h"
 #include "crypto/sha2.h"
@@ -162,9 +161,6 @@ void InlineLoginHandlerChromeOS::SetExtraInitParams(
     base::DictionaryValue& params) {
   const GaiaUrls* const gaia_urls = GaiaUrls::GetInstance();
   params.SetKey("clientId", base::Value(gaia_urls->oauth2_chrome_client_id()));
-  params.SetKey(
-      "platformVersion",
-      base::Value(version_loader::GetVersion(version_loader::VERSION_SHORT)));
 
   const GURL& url = gaia_urls->embedded_setup_chromeos_url(2U);
   params.SetKey("gaiaPath", base::Value(url.path().substr(1)));