Remove LocalizedStrings.{cpp,h}.

They are not used any more.

BUG=298020
TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/26260007

git-svn-id: svn://svn.chromium.org/blink/trunk@159640 bbb929c8-8fbe-4397-9dbb-9b2b20218538