Just to confirm what Rod-IT said.
If you do not intend to keep this system or you have no concern for the data, then you can do whatever you want with it. You do not need to consolidate the snapshots before deleting the system.
My preferred method to remove a system is to right click and select the "Delete from Disk" option rather than unregistering it and messing around with the file system.
IF you care at all about the data or you desire to power it on again in the future, then you will need to properly consolidate the snapshots. Snapshots keep a record of all changes made to a VM Guest. If you were to delete the snapshots you could lose all changes ever made to that system (especially if they are very old). Also, any manual manipulation of the file system almost certainly ensures that you will need to edit the VMX file to repoint the disk definitions.