Revert 3 commits (work will be continued in branch)

Revert "Disabling mcMMO when the config breaks is dumb"

This reverts commit 86e7bfbf89.

Revert "Config validation rewrite part 1"

This reverts commit 16e90da8fd.

Revert "Update changelog"

This reverts commit 0ccd89fad4.

src/main/java/com/gmail/nossr50/util/upgrade/UpgradeManager.java

@@ -19,12 +19,6 @@ public class UpgradeManager extends BukkitConfig {
         loadKeys();
     }
 
-    @Override
-    protected void validateConfigKeys() {
-        //TODO: Rewrite legacy validation code
-        // Look into what needs to change for this
-    }
-
     /**
      * Check if the given {@link UpgradeType} is necessary.
      *