win,tty: avoid regressions in utf-8 handling
win,tty: avoid regressions in utf-8 handling

This code already had special handling for decoding utf-8
characters correctly for the UCS-2 conhost
(trailing incomplete bytes and characters > 0xFFFF).
Rather than trying to duplicate that, we can simply
delete the duplicate code-path and selectively disable
the parts that do not apply.

PR-URL: https://github.com/libuv/libuv/pull/1965
Ref: https://github.com/JuliaLang/julia/issues/27267
Co-authored-by: Mustafa M. <6eb4cc435a2bd8cec35bd771baeccbbf03ee647e@outlook.com>
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso