buffer: harden SlowBuffer creation

PR-URL: https://github.com/nodejs/node/pull/26272
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/buffer.js

@@ -297,8 +297,6 @@ Buffer.allocUnsafeSlow = function allocUnsafeSlow(size) {
 // If --zero-fill-buffers command line argument is set, a zero-filled
 // buffer is returned.
 function SlowBuffer(length) {
-  if (typeof length !== 'number')
-    length = +length;
   assertSize(length);
   return createUnsafeBuffer(length);
 }