buffer: remove TODOs in atob / btoa

Refs: nodejs#38433 (comment)

Author: XadillaX

lib/buffer.js

@@ -1220,8 +1220,6 @@ const lazyInvalidCharError = hideStackFrames((message, name) => {
 });
 
 function btoa(input) {
-  // TODO(@jasnell): The implementation here has not been performance
-  // optimized in any way.
   input = `${input}`;
   for (let n = 0; n < input.length; n++) {
     if (input[n].charCodeAt(0) > 0xff)
@@ -1235,8 +1233,6 @@ const kBase64Digits =
   'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
 
 function atob(input) {
-  // TODO(@jasnell): The implementation here has not been performance
-  // optimized in any way.
   input = `${input}`;
   for (let n = 0; n < input.length; n++) {
     if (!kBase64Digits.includes(input[n]))