Remove BrowserSideNavigation from about://flags

BrowserSideNavigation has launched on all chromium platforms (except Android WebView), and the old
navigation codepath is no longer supported at the Chrome layer. Removing
the option to turn off browser-side navigation in regular Chrome.

BUG=789577

Change-Id: I6e450f1e33108aa5b5cfe5241a7fd3af188d6394
Reviewed-on: https://chromium-review.googlesource.com/796857Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Camille Lamy <clamy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520162}

chrome/browser/about_flags.cc

@@ -3268,9 +3268,6 @@ const FeatureEntry kFeatureEntries[] = {
      flag_descriptions::kEnablePictureInPictureDescription, kOsDesktop,
      SINGLE_VALUE_TYPE(switches::kEnablePictureInPicture)},
 #endif  // !defined(OS_ANDROID)
-    {"browser-side-navigation", flag_descriptions::kBrowserSideNavigationName,
-     flag_descriptions::kBrowserSideNavigationDescription, kOsAll,
-     FEATURE_VALUE_TYPE(features::kBrowserSideNavigation)},
     {"navigation-mojo-response", flag_descriptions::kNavigationMojoResponseName,
      flag_descriptions::kNavigationMojoResponseDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kNavigationMojoResponse)},

chrome/browser/flag_descriptions.cc

@@ -81,10 +81,6 @@ const char kBlockTabUndersDescription[] =
     "Blocks tab-unders in Chrome with some native UI to allow the user to "
     "proceed.";
 
-const char kBrowserSideNavigationName[] = "Enable browser side navigation";
-const char kBrowserSideNavigationDescription[] =
-    "Enable browser side navigation (aka PlzNavigate).";
-
 const char kNavigationMojoResponseName[] = "Navigation response using Mojo";
 const char kNavigationMojoResponseDescription[] =
     "Browser side navigation (aka PlzNavigate) is using blob URLs to deliver "

chrome/browser/flag_descriptions.h

@@ -75,9 +75,6 @@ extern const char kBleAdvertisingInExtensionsDescription[];
 extern const char kBlockTabUndersName[];
 extern const char kBlockTabUndersDescription[];
 
-extern const char kBrowserSideNavigationName[];
-extern const char kBrowserSideNavigationDescription[];
-
 extern const char kNavigationMojoResponseName[];
 extern const char kNavigationMojoResponseDescription[];