Change 'big5' to 'Big5'

Some layout tests and chrome browser tests compare the encoding labels
case-sensitively. Fixing them all takes a while. In the meantime,
change the ICU alias table to use exactly what they expects (Big5).

Also drop big5-hkscs from the alias for Big5 for now. They'll be
unified in another CL.

See the layout test failures for PS #2 at https://codereview.chromium.org/649413002

BUG=412053
TEST=browser_tests --gtest_filter=*ncoding*
TEST=Layout tests : http/tests/misc/char-encod*, fast/encoding/*
R=jsbell@chromium.org
TBR=jsbell@chromium.org

Review URL: https://codereview.chromium.org/654153002

git-svn-id: https://src.chromium.org/chrome/trunk/deps/third_party/icu52@292476 4ff67af0-8c30-449e-8e8b-ad334ec8d88c