siteadmins either see no custom assets

refs FOO-1273
flag=none

masquerade to see all custom assets

TEST PLAN:
  1) visit a custom assets account as siteadmin
  2) custom css and js should not render
  3) masquerade as a user
  4) both custom css and js render

Change-Id: I15c9aa00667d3709656566a76f5fc4ea6cb6828e
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/254357
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Ethan Vizitei <evizitei@instructure.com>
Product-Review: Ethan Vizitei <evizitei@instructure.com>

app/helpers/application_helper.rb

@@ -741,11 +741,6 @@ module ApplicationHelper
     @current_pseudonym.works_for_account?(brand_config_account, ignore_types: [:site_admin])
   end
 
-  def has_custom_js
-    @domain_root_account.allow_global_includes? &&
-      active_brand_config(ignore_high_contrast_preference: true)&.css_and_js_overrides&.[](:js_overrides).present?
-  end
-
   def include_account_js
     return if params[:global_includes] == '0' || !@domain_root_account
     return unless pseudonym_can_see_custom_assets
@@ -775,7 +770,7 @@ module ApplicationHelper
 
   def include_account_css
     return if disable_account_css?
-    return if has_custom_js && !pseudonym_can_see_custom_assets
+    return unless pseudonym_can_see_custom_assets
 
     includes = if @domain_root_account.allow_global_includes? && (abc = active_brand_config(ignore_high_contrast_preference: true))
       abc.css_and_js_overrides[:css_overrides]

spec/helpers/application_helper_spec.rb

@@ -269,10 +269,9 @@ describe ApplicationHelper do
             allow(@current_pseudonym).to receive(:works_for_account?).and_return(false)
           end
 
-          it "still renders if there's no JS" do
+          it "won't render only JS" do
             allow(helper).to receive(:active_brand_config).and_return BrandConfig.create!(css_overrides: 'https://example.com/path/to/overrides.css')
-            expect(helper.include_account_css).to_not be_nil
-            expect(helper.include_account_css).to match %r{overrides.css}
+            expect(helper.include_account_css).to be_nil
           end
 
           it "will not render if there's javacscript" do