Use delete[] on flexible structs allocated with new[] in SSTIO
Use delete[] on flexible structs allocated with new[] in SSTIO

- The SST ioctl interface accepts structs with flexible size. The size
  of the struct is dynamically determined based on the payload, then the
  struct is allocated by GEOPM with new[size] and put in a unique_ptr<>.
- Since the unique_ptr<> does not contain an array (but a struct with
  variable size), the default deleter operation is `delete`. This change
  overrides the unique_ptr<> deleter to use delete[] instead, which
  correctly pairs with the new[] operation used to allocate the
  variable-sized struct.
- Resolves #2440

geopm/geopm,cmcantalupo/geopm,cmcantalupo/geopm,cmcantalupo/geopm,geopm/geopm,cmcantalupo/geopm,geopm/geopm,geopm/geopm,cmcantalupo/geopm,geopm/geopm