Revert membership debug handling in IPN

Revert membership debug handling in IPN

A looong time ago we added handling for the possibility of messed up memberships going through
the paypal IPN. https://github.com/civicrm/civicrm-core/pull/15053

At the time we added a lot of debug to see if it was ever hit as the handling was
an attempt to figure out a bug that we couldn't reproduce. We never got any
evidence the debug was hit or the fix helped - but
it does create a lot of code complexity and makes clean up
more difficult so
this removes it again....