Convert editing/inserting/insert-paragraph-0[1-5].html to use w3c test harness

This patch converts "editing/inserting/insert-paragraph-0[1-5].html" to use w3c
test harness and consolidates into "insert_paragraph.html" to simplify test
case for ease of maintenance.

This patch is a preparation of getting rid of grammar checking feature.

Review-Url: https://codereview.chromium.org/2175233002
Cr-Commit-Position: refs/heads/master@{#407718}
30 files changed