Revert "Clean up ApiEditPage content handler undo logic"

Revert "Clean up ApiEditPage content handler undo logic"

This reverts commit 01564dcbf76cd279c88320f96f0844cfadf4f7c9.

Reason for revert: I find the empty case far clearer as to intention than this change, and I doubt this is such a hot path that optimization should take precedence over clarity. If we really want to get rid of the empty case, I'd have structured it somewhat clearly as

 if (
     // always allow undo via api, T230702
     !( $params['undo'] > 0 ) &&
     // [something else here to explain this clause]
     $contentHandler->supportsDirectApiEditing() === false
 ) {

But even that is IMO less clear. At the very least this seems to deserve more discussion.

Bug: T230702
Change-Id: Icc16250faad31abf7308c4af9be2e7658540346c