Remove memcache stampede from general settings file

Problem/Motivation

The stampede option for memcache was removed 4 years ago. We best remove the settings from our general settings file to avoid confusion.

// Enable stampede protection.
$settings['memcache']['stampede_protection'] = TRUE;

see: https://git.drupalcode.org/project/memcache/-/commit/7bba7982c129a0c0632...