Avoid duplicate checks for Heroku deploys

The `render` function now has its own checks to avoid using the HTML from the fixture files, so we can consolidate them into one and avoid having two slightly different checks in different parts of the code.

packages/govuk-frontend-review/src/app.mjs

@@ -218,9 +218,7 @@ export default async () => {
       const componentView = render(componentName, {
         context: fixture.options,
         env,
-
-        // Skip Nunjucks render from cache in development
-        fixture: flags.isDevelopment ? undefined : fixture
+        fixture
       })
 
       let bodyClasses = 'app-template__body'

shared/lib/components.js

@@ -155,8 +155,10 @@ function render(componentName, options) {
   const macroName = componentNameToMacroName(componentName)
   const macroPath = `govuk/components/${componentName}/macro.njk`
 
-  // Use built fixtures (if they exist) on CI to optimise for speed
-  if (process.env.CI === 'true' && options?.fixture?.html) {
+  // On Heroku / CI we know we're running against an up-to-date build so we can
+  // use the generated HTML from the component JSON (where it exists) to make
+  // things faster
+  if ((process.env.HEROKU_APP || process.env.CI) && options?.fixture?.html) {
     return options.fixture.html
   }