Remove unused header file core/editing/EditorInsertAction.h

This patch removes unused header file core/editing/EditorInsertAction.h, which is obsoleted by r159279, https://src.chromium.org/viewvc/blink?view=revision&revision=159279, remove unused editing related member functions from WebViewClient.

BUG=302013
TEST=n/a; no behavior changes, existing tests covers this changes.
R=tkent@chromium.org

Review URL: https://codereview.chromium.org/26552007

git-svn-id: svn://svn.chromium.org/blink/trunk@159320 bbb929c8-8fbe-4397-9dbb-9b2b20218538