Elim detached_panel type and update chrome.windows documentation

This also eliminates references to --enable-panels

BUG=467808
For random OWNERS of minor changes:
TBR=rdevlin.cronin@chromium.org

Review-Url: https://chromiumcodereview.appspot.com/2424143002
Cr-Commit-Position: refs/heads/master@{#426365}
6 files changed