This reverts commit 4736c31.
I.e. revert the revert.

PR-URL: libuv#2501
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Saúl Ibarra Corretgé <s@saghul.net>
Reviewed-By: Jameson Nash <vtjnash+github@gmail.com>
(cherry picked from commit fd2ce38)

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: libuv#1965
Ref: JuliaLang/julia#27267
Co-authored-by: Mustafa M. <mus-m@outlook.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
(cherry picked from commit 3016fbc)

PR-URL: libuv#1884
Co-authored-by: Bert Belder <bertbelder@gmail.com>
Co-authored-by: Jameson Nash <vtjnash@gmail.com>
Reviewed-By: Jameson Nash <vtjnash@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <s@saghul.net>
(cherry picked from commit 73ca4ac)

PR-URL: libuv#1884
Refs: libuv#1874
Co-authored-by: Bert Belder <bertbelder@gmail.com>
Co-authored-by: Jameson Nash <vtjnash@gmail.com>
Reviewed-By: Jameson Nash <vtjnash@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <s@saghul.net>
(cherry picked from commit 288a067)