Manual:$wgActions

Details
Array of allowed values for the "action" parameter for normal pages.

Syntax is:

Load the specified class which subclasses  Load the class FooAction which subclasses Action The action is disabled; show an error message

Disable an action
To disable an action just add the following e.g. for the "raw" action to your "LocalSettings.php" file:

Unsetting core actions will probably cause things to complain loudly.