Revert "md5 and utf_encode js libraries"

## What does this MR do?

Remove two unused JavaScript libraries (`md5.js` and `utf8_encode.js`).

## Why was this MR needed?

Those libraries were not used anymore:

```
$ find app/ lib/ -name '*.js' -exec grep --perl-regexp --with-filename '(md5|utf8_encode)' {} \;
app/assets/javascripts/lib/utils/utf8_encode.js:function utf8_encode (argString) {
app/assets/javascripts/lib/utils/utf8_encode.js:  // *     example 1: utf8_encode('Kevin van Zonneveld');
app/assets/javascripts/lib/utils/md5.js:function md5 (str) {
app/assets/javascripts/lib/utils/md5.js:  // -    depends on: utf8_encode
app/assets/javascripts/lib/utils/md5.js:  // *     example 1: md5('Kevin van Zonneveld');
app/assets/javascripts/lib/utils/md5.js:  str = this.utf8_encode(str);
```


See merge request !5613