Remove unused ALLOW_INCOGNITO_CUSTOM_TABS_FROM_THIRD_PARTY switch.

Just clean up.

Bug: 1023759
Change-Id: I6e13a4fb072e1e4645c8d1626b90f5030921ce02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1925065
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Auto-Submit: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716973}

chrome/android/java_templates/ChromeSwitches.java.tmpl

@@ -172,12 +172,6 @@ public abstract class ChromeSwitches {{
      */
     public static final String ENABLE_INCOGNITO_CUSTOM_TABS = "enable-incognito-custom-tabs";
 
-    /**
-     * Allows third-party apps to launch incognito custom tabs.
-     */
-    public static final String ALLOW_INCOGNITO_CUSTOM_TABS_FROM_THIRD_PARTY =
-            "allow-incognito-custom-tabs-from-third-party";
-
     /** Prevents use of first-party Google Play Services. */
     public static final String DISABLE_FIRST_PARTY_GOOGLE_PLAY_SERVICES_FOR_TESTING =
             "disable-first-party-google-play-services-for-testing";