Remove OutputAssets::new if condition (vercel/turborepo#6195)

### Description

It's unneeded, the input param caching will correctly handle this case
already.

vercel/turborepo#6194 (comment)

### Testing Instructions

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Closes WEB-1794

crates/turbopack-core/src/output.rs

@@ -25,16 +25,13 @@ pub struct OutputAssets(Vec<Vc<Box<dyn OutputAsset>>>);
 impl OutputAssets {
     #[turbo_tasks::function]
     pub fn new(assets: Vec<Vc<Box<dyn OutputAsset>>>) -> Vc<Self> {
-        if assets.is_empty() {
-            OutputAssets::empty()
-        } else {
-            Vc::cell(assets)
-        }
+        Vc::cell(assets)
     }
+}
 
-    #[turbo_tasks::function]
+impl OutputAssets {
     pub fn empty() -> Vc<Self> {
-        Vc::cell(vec![])
+        Self::new(vec![])
     }
 }