Enable setVisibleOnAllWorkspaces on stable.

This was made stable in https://codereview.chromium.org/866893003 but
that CL missed this is-dev-channel check.

BUG=495039,384644

Review URL: https://codereview.chromium.org/1170843005

Cr-Commit-Position: refs/heads/master@{#333648}

extensions/browser/api/app_current_window_internal/app_current_window_internal_api.cc

@@ -375,11 +375,6 @@ bool AppCurrentWindowInternalSetAlwaysOnTopFunction::RunWithWindow(
 
 bool AppCurrentWindowInternalSetVisibleOnAllWorkspacesFunction::RunWithWindow(
     AppWindow* window) {
-  if (AppWindowClient::Get()->IsCurrentChannelOlderThanDev()) {
-    error_ = kDevChannelOnly;
-    return false;
-  }
-
   scoped_ptr<SetVisibleOnAllWorkspaces::Params> params(
       SetVisibleOnAllWorkspaces::Params::Create(*args_));
   CHECK(params.get());