benchmark: remove unreachable code from crypto/hash-stream-creation

`hash.digest('buffer')` has returned a Buffer and not a string since at
least Node.js 0.10.6. The benchmark, as it is written, will not work on
any version of Node.js prior to 16.x (due to `Object.hasOwn()`) and
certainly won't run on versions earlier than 0.10.6 due to const/let and
probably other things. Remove impossible-to-reach code intended to
accommodate Node.js earlier than 0.10.6.

PR-URL: #41535
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott

benchmark/crypto/hash-stream-creation.js

@@ -52,11 +52,7 @@ function legacyWrite(algo, message, encoding, writes, len, outEnc) {
   while (writes-- > 0) {
     const h = crypto.createHash(algo);
     h.update(message, encoding);
-    let res = h.digest(outEnc);
-
-    // Include buffer creation costs for older versions
-    if (outEnc === 'buffer' && typeof res === 'string')
-      res = Buffer.from(res, 'binary');
+    h.digest(outEnc);
   }
 
   bench.end(gbits);