If you don't mind a bit of a brute force attack, Microsoft Word can do this. I'd recommend recording a macro, because it's pretty tedious, and that way you only need to go through the whole process once for each file type, and after that you can just press a button and have it all done by magic.
The key is to know that in the find and replace function, ^? represents any character.
So paste your HTML code into Word, and then do a serious of find and replace operations, in each case replacing the string with an empty string.
Start with <!-- ^? --> then <!-- ^?^? --> then <!-- ^?^?^? --> and so on.
It helps if you know what the shortest and longest comments you've used are, and that way if you know that you've never left a comment with fewer than three characters, you can miss the first couple of replacements out.
Same principle for comments in other languages, except that obviously you have to change the delimiters.