Remove unused transparency display item functions.
Remove unused transparency display item functions.

Transparency display items have been replaced by the new compositing
display items and are no longer needed. This patch also fixes an old
fixme by removing FILTER_DISPLAY_ITEM_USES_FILTER_OPERATIONS.

Review URL: https://codereview.chromium.org/953143003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@190854 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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