Captive portal interstitial: Use the same string for page title and header.

I've noticed that the localization of the strings are done differently, so
it's better to use the same string for both.

BUG=

Review URL: https://codereview.chromium.org/881973002

Cr-Commit-Position: refs/heads/master@{#313602}

chrome/app/generated_resources.grd

@@ -9875,12 +9875,6 @@ I don't think this site should be blocked!
       </if>
 
       <!-- Captive portal interstitial -->
-      <message name="IDS_CAPTIVE_PORTAL_TITLE_WIRED" desc="Title in the error page when a secure request is blocked because the network is redirecting the request to another page until the user logs in">
-        Connect to Network
-      </message>
-      <message name="IDS_CAPTIVE_PORTAL_TITLE_WIFI" desc="Title in the error page when a secure request is blocked because the Wi-fi is redirecting the request to another page until the user logs in">
-        Connect to Wi-Fi
-      </message>
       <message name="IDS_CAPTIVE_PORTAL_HEADING_WIRED" desc="Heading in the error page when a secure request is blocked because a captive portal is manipulating a wired connection (e.g. ethernet)">
         Connect to network
       </message>

chrome/browser/ssl/captive_portal_blocking_page.cc

@@ -97,8 +97,8 @@ void CaptivePortalBlockingPage::PopulateInterstitialStrings(
   load_time_data->SetString("tabTitle",
       l10n_util::GetStringUTF16(
           is_wifi_connection_ ?
-          IDS_CAPTIVE_PORTAL_TITLE_WIFI :
-          IDS_CAPTIVE_PORTAL_TITLE_WIRED));
+          IDS_CAPTIVE_PORTAL_HEADING_WIFI :
+          IDS_CAPTIVE_PORTAL_HEADING_WIRED));
   load_time_data->SetString("heading",
       l10n_util::GetStringUTF16(
           is_wifi_connection_ ?