Rip out infrastructure for bloatedCharacters

Now that we cannot create Strings with bloatedCharacters, we can rip out the
infrastructure that supports them. This CL saves 92 kB of binary.

R=eseidel@chromium.org
BUG=254708

Review URL: https://codereview.chromium.org/19638012

git-svn-id: svn://svn.chromium.org/blink/trunk@154562 bbb929c8-8fbe-4397-9dbb-9b2b20218538