buffer: remove TODOs in atob / btoa

Refs: #38433 (comment)

PR-URL: #38548
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Zijian Liu <lxxyxzj@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/buffer.js

@@ -1217,8 +1217,9 @@ const lazyInvalidCharError = hideStackFrames((message, name) => {
 });
 
 function btoa(input) {
-  // TODO(@jasnell): The implementation here has not been performance
-  // optimized in any way.
+  // The implementation here has not been performance optimized in any way and
+  // should not be.
+  // Refs: https://github.com/nodejs/node/pull/38433#issuecomment-828426932
   input = `${input}`;
   for (let n = 0; n < input.length; n++) {
     if (input[n].charCodeAt(0) > 0xff)
@@ -1232,8 +1233,9 @@ const kBase64Digits =
   'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
 
 function atob(input) {
-  // TODO(@jasnell): The implementation here has not been performance
-  // optimized in any way.
+  // The implementation here has not been performance optimized in any way and
+  // should not be.
+  // Refs: https://github.com/nodejs/node/pull/38433#issuecomment-828426932
   input = `${input}`;
   for (let n = 0; n < input.length; n++) {
     if (!kBase64Digits.includes(input[n]))