code cleanup: delete MPP_PREP and REBUILD

Development description

As decided in March during the Merge fiesta code cleanup session (&11) we decided that MPP_PREP and REBUILD are useless (same feature already into NEMO itself or better tool with same functionality available) and need to be removed.

Code implementation

No complication: simply remove the directory and update the tools README if needed

Documentation updates

Update tool README if needed.

Edited Oct 26, 2023 by Daley Calvert

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information