build: Intl: deps: bump ICU to 56.1 (GA)

* ICU 56 was just released yesterday. Update to it.
* Notable changes: Unicode 8, CLDR 28, 2-3x number format perf,
  20% improvement in Collator startup
  * more at http://site.icu-project.org/download/56 or in #2917

Also:

* cleanup out/**/*.d and deps/icu  on "make clean"
* cleanup deps/icu on "vcbuild clean"

When building from an non-clean directory, it's important to
run `make clean` or `vcbuild clean` to remove the existing
ICU 55 from the deps path before building.

Fixes: https://github.com/nodejs/node/issues/2917
PR-URL: https://github.com/nodejs/node/pull/3281


Reviewed-By: James M Snell <jasnell@gmail.com>