Re-enable QR code sharing for a URL

Fixes brave/brave-browser#15900

Also includes cleanup; removes obsolete flags added with
#5435 (this experiment was
removed and enabled by default with Chromium 91)

app/brave_main_delegate.cc

@@ -22,7 +22,6 @@
 #include "brave/renderer/brave_content_renderer_client.h"
 #include "brave/utility/brave_content_utility_client.h"
 #include "build/build_config.h"
-#include "chrome/browser/sharing/features.h"
 #include "chrome/browser/ui/ui_features.h"
 #include "chrome/common/chrome_features.h"
 #include "chrome/common/chrome_paths.h"
@@ -220,12 +219,10 @@ bool BraveMainDelegate::BasicStartupComplete(int* exit_code) {
     features::kSignedExchangePrefetchCacheForNavigations.name,
     features::kSignedExchangeSubresourcePrefetch.name,
     features::kSubresourceWebBundles.name,
-    features::kTabHoverCards.name,
     features::kWebOTP.name,
     federated_learning::kFederatedLearningOfCohorts.name,
     federated_learning::kFlocIdComputedEventLogging.name,
     federated_learning::kFlocIdSortingLshBasedComputation.name,
-    kSharingQRCodeGenerator.name,
     network_time::kNetworkTimeServiceQuerying.name,
     safe_browsing::kEnhancedProtection.name,
     safe_browsing::kEnhancedProtectionMessageInInterstitials.name,

app/brave_main_delegate_browsertest.cc

@@ -4,7 +4,6 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "chrome/browser/domain_reliability/service_factory.h"
-#include "chrome/browser/sharing/features.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/profile_picker.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
@@ -78,13 +77,11 @@ IN_PROC_BROWSER_TEST_F(BraveMainDelegateBrowserTest, DisabledFeatures) {
       &features::kSignedExchangePrefetchCacheForNavigations,
       &features::kSignedExchangeSubresourcePrefetch,
       &features::kSubresourceWebBundles,
-      &features::kTabHoverCards,
       &features::kWebOTP,
       &federated_learning::kFederatedLearningOfCohorts,
       &federated_learning::kFlocIdComputedEventLogging,
       &federated_learning::kFlocIdSortingLshBasedComputation,
       &kEnableProfilePickerOnStartupFeature,
-      &kSharingQRCodeGenerator,
       &network_time::kNetworkTimeServiceQuerying,
       &safe_browsing::kEnhancedProtection,
       &safe_browsing::kEnhancedProtectionMessageInInterstitials,