remove support for old platforms

I think it's time to tidy up some old legacy code

You still have hacks for IE8

Line 24 in 9c79ba6

// Use XDomainRequest for IE8 if enablesXDR is true

nobody is using ie < 11 anymore
and ie 11 is down to less than 0.7% global usage

Hi! 0.7 % of the global Internet population is still a lot though, I'm not sure we can just ignore them. What do you think?

Regarding the IE8-specific code, I think we can indeed remove it, as it's quite hard to test/provide a working bundle.

speaking of xhr, it is not available in web workers so if you want to use long polling in workers, then u have to use fetch.
But i guess websocket is pretty much preferred over long polling now.
Also it looks like fetch is coming to NodeJS pretty soon (Deno already has it)

Closed by c656192.