Don't schedule a style recalc when clearing out placeholder styles

Previously we would schedule a style recalc when clearing out placeholder
styles. However, we're just going to run the style recalc immediately anyway.

In reality, we should remove placeholder styles entirely, but that's tied up in
some plugin complexity.

R=esprehn@chromium.org
BUG=343564

Review URL: https://codereview.chromium.org/164503003

git-svn-id: svn://svn.chromium.org/blink/trunk@167137 bbb929c8-8fbe-4397-9dbb-9b2b20218538