Breaking: #69904 - Remove Setting diff_path from DefaultConfiguration

See Issue #69904

Description

Creating a diff view of text has been replaced with a PHP library instead of using diff on the command line. Thus we no longer need to be able to configure the path.

Impact

The setting [BE][diff_path] will no longer have any effect.

Affected Installations

Any Installation that had to define a path different than diff

Migration

Delete the line from LocalConfiguration.php if the UpgradeWizard should fail to do so.