Remove removed uniscribe files from blink_platform.gypi

Clean up blink_platform.gypi and remove references to files that are
no longer part of the build.

TBR=leviw@chromium.org
BUG=313423

Review URL: https://codereview.chromium.org/213163002

git-svn-id: svn://svn.chromium.org/blink/trunk@170078 bbb929c8-8fbe-4397-9dbb-9b2b20218538