first version was kind of a hack; the current implementation of the
procedure to extract the required symbols is much cleaner.
Reworked creation of MMS files, avoiding a number of temporary files
which were created in the previous version.
Further work on creating descrip.mms files on the fly.
* builds/vms/descrip.mms, src/autohint/descrip.mms,
src/type1/descrip.mms: Removed.