[sms] Remove the extra check for the Experimental Web Platform Feature

The rollout of SmsReceiver is controlled via the origin trials
mechanism [1], so, to enable it on stable, the flag isn't necessary
anymore to gate the deployment.

[1] https://cs.chromium.org/chromium/src/third_party/blink/renderer/platform/runtime_enabled_features.json5?type=cs&q=SmsReceiver+feature&sq=package:chromium&g=0&l=1563

Bug: 1007212
Change-Id: I581b5ba13c281c334a9961caf21bda5608064365
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1823698Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Sam Goto <goto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699540}

content/browser/frame_host/render_frame_host_impl.cc

@@ -4502,9 +4502,7 @@ void RenderFrameHostImpl::RegisterMojoInterfaces() {
       &GetRestrictedCookieManager, base::Unretained(this),
       GetProcess()->GetID(), routing_id_, GetProcess()->GetStoragePartition()));
 
-  if (base::FeatureList::IsEnabled(features::kSmsReceiver) &&
-      base::CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kEnableExperimentalWebPlatformFeatures)) {
+  if (base::FeatureList::IsEnabled(features::kSmsReceiver)) {
     registry_->AddInterface(base::BindRepeating(
         &RenderFrameHostImpl::BindSmsReceiverReceiver, base::Unretained(this)));
   }