Revert r58635 and related, unnecessary and incorrect use of the hook mechanism

docs/hooks.txt

@@ -552,11 +552,6 @@ $user: the user who did the block (not the one being blocked)
 'BookInformation': Before information output on Special:Booksources
 $isbn: ISBN to show information for
 $output: OutputPage object in use
-
-'CacheHeadersAfterSet': after cache headers have been set in 
-OutputPage::sendCacheControl, so they can be overridden without 
-disabling output method
-$out: OutputPage instance
  
 'CategoryPageView': before viewing a categorypage in CategoryPage::view
 $catpage: CategoryPage instance

includes/OutputPage.php

@@ -1401,7 +1401,6 @@ class OutputPage {
 			$response->header( 'Cache-Control: no-cache, no-store, max-age=0, must-revalidate' );
 			$response->header( 'Pragma: no-cache' );
 		}
-		wfRunHooks('CacheHeadersAfterSet', array( $this ) );
 	}
 
 	/**