crypto: remove useless if statement

The if statement in `ECDH.getPublicKey` is useless. This change
is to remove it.

PR-URL: #15041
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>

Author: starkwang

lib/internal/crypto/diffiehellman.js

@@ -191,8 +191,6 @@ ECDH.prototype.generateKeys = function generateKeys(encoding, format) {
 ECDH.prototype.getPublicKey = function getPublicKey(encoding, format) {
   var f;
   if (format) {
-    if (typeof format === 'number')
-      f = format;
     if (format === 'compressed')
       f = POINT_CONVERSION_COMPRESSED;
     else if (format === 'hybrid')