buffer: remove unreachable code

Remove unreachable code from lib/buffer.js.

PR-URL: #27445
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: Trott

lib/buffer.js

@@ -894,11 +894,7 @@ Buffer.prototype.write = function write(string, offset, length, encoding) {
 
   // Buffer#write(string, offset[, length][, encoding])
   } else {
-    if (offset === undefined) {
-      offset = 0;
-    } else {
-      validateInt32(offset, 'offset', 0, this.length);
-    }
+    validateInt32(offset, 'offset', 0, this.length);
 
     const remaining = this.length - offset;