simplify main substituteAtApply call again

Now that we are substituting `@apply` in the correct order via a
topological sort, it means that we don't have to try and first handle
all `@utility` at-rules. This will already be handled in the correct
order.

Author: RobinMalfait

packages/tailwindcss/src/index.ts

@@ -538,24 +538,15 @@ async function parseCss(
     node.context = {}
   }
 
-  // Post-process `@utility` nodes.
-  //
-  // We have to do this as a separate step because if we replace the `@utility`
-  // nodes when we collect it in the system, then we can't substitute the
-  // `@apply` at-rules anymore.
-  //
-  // We also can't substitute the `@apply` at-rules while collecting the
-  // `@utility` rules, because if it relies on a utility that is defined later,
-  // then we wouldn't be able to resolve the applied utility.
-  //
-  // Lastly, we can't rely on the single `substituteAtApply` call at the end
-  // because this replaces `@apply`, but won't replace `@apply` if we injected
-  // an `@apply`.
+  features |= substituteFunctions(ast, designSystem.resolveThemeValue)
+  features |= substituteAtApply(ast, designSystem)
+
+  // Remove `@utility`, we couldn't replace it before yet because we had to
+  // handle the nested `@apply` at-rules first.
   walk(ast, (node, { replaceWith }) => {
     if (node.kind !== 'at-rule') return
 
     if (node.name === '@utility') {
-      substituteAtApply(node.nodes, designSystem)
       replaceWith([])
     }
 
@@ -564,11 +555,6 @@ async function parseCss(
     return WalkAction.Skip
   })
 
-  // Replace `@apply` rules with the actual utility classes.
-  features |= substituteAtApply(ast, designSystem)
-
-  features |= substituteFunctions(ast, designSystem.resolveThemeValue)
-
   return {
     designSystem,
     ast,