Remove a static initializer in region.cpp

region.cpp has an unnecessary static initializer for a type
UnicodeString and triggers a 'si check' failure.

Upstream bug: http://bugs.icu-project.org/trac/ticket/12408

BUG=575007
TEST=`tools/linux/dump-static-initializers.py chrome` (static build) does not have an entry from region.cpp
TEST=`tools/linux/dump-static-initializers.py libicui18n.so` (shared build) has no entry.
TBR=thakis@chromium.org

Review URL: https://codereview.chromium.org/1816843002 .
3 files changed