Remove exclamation mark from bookmark bubble title

"Bookmark added!" => "Bookmark added"

ainslie@ says it doesn't belong.

BUG=none

Review-Url: https://codereview.chromium.org/2142103002
Cr-Commit-Position: refs/heads/master@{#405191}
1 file changed