Remove some legacy things?

[jimmywarting]

Flash and older ie is pretty much dead now... So i was wondering if things such as applet, object and conditional comments such as Conditional ie Comment could be removed now. https://github.com/terser/html-minifier-terser/blob/5caba1bfa0dd32656bc26ef8ba3eadd51a890c67/src/htmlminifier.js#L522-L531

[sibiraj-s]

Sounds okay to me. but it calls for a new major.

Also, Sometimes I think of re-writing the package with htmlparser2 and make it more modern. but it replicating them is not as easy as it seems. dropping some old and redundant features might enable that in coming days may be

[markjaquith]

Please don't remove conditional comments. For better or worse, they're part of the HTML landscape, and stripping them out will break things. People write them for purposes other than IE, and expect them to be present in the HTML output.