We now have a builtin that can do URL escaping so use it. I can't find
any uses of our private `__fish_urlencode` function in any Oh-My-Fish or
Fisherman code so remove it.
In the C/POSIX locale EOF on the tty wasn't handled correctly due to a change
a few months ago to fix an unrelated problem with that locale. What is
surprising is that the core fish code doesn't explicitly depend on
input_common_readch returning WEOF if a character isn't seen within
`wait_on_escape_ms` after an escape.
Fixes#3214
