Remove unused includes from core/{editing,fileapi,history,html}

Continue removing unused includes as suggested by include-what-you-use.
I've manually looked through the changes here so all the removals should
be actually unused.

BUG=242216

Review URL: https://chromiumcodereview.appspot.com/17388003

git-svn-id: svn://svn.chromium.org/blink/trunk@152932 bbb929c8-8fbe-4397-9dbb-9b2b20218538