Remove keyIdentifier.

KeyboardEvent.key and KeyboardEvent.code are the replacements for
KeyboardEvent.keyIdentifier.

Approved intent to remove: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/fqnFyoDCOaA/s4WIxZPqAAAJ

BUG=607349

Review-Url: https://codereview.chromium.org/2120153003
Cr-Commit-Position: refs/heads/master@{#404015}
55 files changed