crypto: remove default encoding from Hash/Hmac

getDefaultEncoding() always returns 'buffer' in Node.js 20. It requires
some careful justification but the default encoding can be eliminated
from hash.js entirely. The reasoning is almost identical with that in
nodejs#49145 so I won't repeat it here.

Refs: nodejs#47182

lib/internal/crypto/hash.js

@@ -14,7 +14,6 @@ const {
 } = internalBinding('crypto');
 
 const {
-  getDefaultEncoding,
   getStringOption,
   jobPromise,
   normalizeHashName,
@@ -95,8 +94,6 @@ Hash.prototype._flush = function _flush(callback) {
 };
 
 Hash.prototype.update = function update(data, encoding) {
-  encoding = encoding || getDefaultEncoding();
-
   const state = this[kState];
   if (state[kFinalized])
     throw new ERR_CRYPTO_HASH_FINALIZED();
@@ -118,10 +115,9 @@ Hash.prototype.digest = function digest(outputEncoding) {
   const state = this[kState];
   if (state[kFinalized])
     throw new ERR_CRYPTO_HASH_FINALIZED();
-  outputEncoding = outputEncoding || getDefaultEncoding();
 
-  // Explicit conversion for backward compatibility.
-  const ret = this[kHandle].digest(`${outputEncoding}`);
+  // Explicit conversion of truthy values for backward compatibility.
+  const ret = this[kHandle].digest(outputEncoding && `${outputEncoding}`);
   state[kFinalized] = true;
   return ret;
 };
@@ -147,15 +143,16 @@ Hmac.prototype.update = Hash.prototype.update;
 
 Hmac.prototype.digest = function digest(outputEncoding) {
   const state = this[kState];
-  outputEncoding = outputEncoding || getDefaultEncoding();
 
   if (state[kFinalized]) {
     const buf = Buffer.from('');
-    return outputEncoding === 'buffer' ? buf : buf.toString(outputEncoding);
+    if (outputEncoding && outputEncoding !== 'buffer')
+      return buf.toString(outputEncoding);
+    return buf;
   }
 
-  // Explicit conversion for backward compatibility.
-  const ret = this[kHandle].digest(`${outputEncoding}`);
+  // Explicit conversion of truthy values for backward compatibility.
+  const ret = this[kHandle].digest(outputEncoding && `${outputEncoding}`);
   state[kFinalized] = true;
   return ret;
 };