FileAPI: Remove TODOs around readAsBinaryString - it's back in the spec

FileReader.readAsBinaryString() was removed from the spec after typed
arrays became a thing. But all browsers kept shipping it, and it looks
risky to remove, so it was added back to the spec. Remove the use
counters and TODOs in the IDL files.

R=foolip@chromium.org

Review-Url: https://codereview.chromium.org/2171953002
Cr-Commit-Position: refs/heads/master@{#407202}
3 files changed