[getUserMedia, ImageCapture] Cleanup a TODO to remove GetUserMedia flag.

The runtime flag GetUserMedia is no longer needed as
navigator.getUserMedia shipped in M53

BUG=607439

Change-Id: Id58babefdb6611e27021d0b2b1af2119d785bf8a
Reviewed-on: https://chromium-review.googlesource.com/c/1296594Reviewed-by: Miguel Casas <mcasas@chromium.org>
Commit-Queue: Rijubrata Bhaumik <rijubrata.bhaumik@intel.com>
Cr-Commit-Position: refs/heads/master@{#602336}

content/browser/webrtc/webrtc_image_capture_browsertest.cc

@@ -87,10 +87,6 @@ class WebRtcImageCaptureBrowserTestBase
     ASSERT_FALSE(base::CommandLine::ForCurrentProcess()->HasSwitch(
         switches::kUseFakeDeviceForMediaStream));
 
-    // "GetUserMedia": enables navigator.mediaDevices.getUserMedia();
-    // TODO(mcasas): remove GetUserMedia after https://crbug.com/503227.
-    base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
-        switches::kEnableBlinkFeatures, "GetUserMedia");
   }
 
   void SetUp() override {