[icu] Use char16_t on non-Windows platforms

Following https://crrev.com/c/2599088 Chromium no longer requires UChar
and base::char16 to be exactly the same type. This now allows dropping
the UCHAR_TYPE override for non-Windows platforms, making char16_t the
default UTF16 character type.

Bug: chromium:911896
Change-Id: I5d1e6dc644c16cc31318ea9d9cf89b114900e061
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2617781
Reviewed-by: Frank Tang <ftang@chromium.org>
1 file changed