Remove lots of old blur plumbing.

window.blur() was actually made a no-op in 2012:
https://chromium.googlesource.com/chromium/blink/+/21a68ec34dd297e3e3a468084528ec6dc95e3246

so all the IPC and machinery to make it work is now dead code.

The RenderViewHost::Blur() method might be dead now too, but it's also used by
a guest view test.

Review URL: https://codereview.chromium.org/1345343003

Cr-Commit-Position: refs/heads/master@{#354667}
27 files changed