Revert "Make $civicrm_paths less sensitive to trailing slashes. Add tests."

Revert "Make $civicrm_paths less sensitive to trailing slashes. Add tests."

This is currently causing breakage on wordpress sites where clean urls are not enabled.

Compare the 2 urls below - the top one has an extra (breaking) slash added by this PR.

I propose a quick revert  & patch release followed by 'the right' fix at a slower pace
/wp-admin/admin.php/?page=CiviCRM&q=civicrm%2Fupgrade%2Fqueue%2Fajax%2FrunNext
/wp-admin/admin.php?page=CiviCRM&q=civicrm%2Fupgrade%2Fqueue%2Fajax%2FrunNext

This reverts commit 232fdd3dfac4ea09749d7f178818139514e48e38.