How to Remove "Edit Summary" Off Editor
You can actually disable user's ability to provide summary. I found this while pursuing the first solution:

Administration » Structure » Content types » Basic page

you should see "Manage Fields" tab. Click on it, and you should see a table. The row for Body should show Widget Type as "Text area with a summary" which is a link that allows you to edit it.

Rather than changing the Widget Type which is not possible if you already have one or more entries, go to the "Edit" tab.

About half-way down the tab is a checkbox: "Summary input"
("This allows authors to input an explicit summary..."). Uncheck it, and save. Your content edit page for Basic Page should be free of "Edit summary" options.