make canvas:compile_assets_dev run webpack

Change-Id: Iab62455a896c6a480ab5bd09403d8c341b0b0468
Reviewed-on: https://gerrit.instructure.com/105064
Tested-by: Jenkins
Reviewed-by: Omar Khan <okhan@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>
QA-Review: Simon Williams <simon@instructure.com>

lib/tasks/canvas.rake

@@ -116,7 +116,6 @@ namespace :canvas do
   task :compile_assets_dev do
     ENV["COMPILE_ASSETS_NPM_INSTALL"] = "0"
     ENV["COMPILE_ASSETS_STYLEGUIDE"] = "0"
-    ENV["COMPILE_ASSETS_BUILD_JS"] = "0"
     ENV["COMPILE_ASSETS_API_DOCS"] = "0"
     Rake::Task['canvas:compile_assets'].invoke
   end