Convert editing/deleting/delete-block-merge-contents-0{18,19,20,21}.html to use w3c test harness
This patch converts "editing/deleting/delete-block-merge-contents-0{18,19,20,21}.html" to
use w3c test harness to simplify test script for improving readability, and
consolidates into "delete_block_merge_end_of_line.html" since samples of them
are similar.
BUG=n/a
TEST=n/a; no behavior changes
Committed:
https://crrev.com/fe6da08d78aa26381effc626b952023a99a5da93
Cr-Commit-Position: refs/heads/master@{#412794}