Remove rocksdb in preparation for subtree add
Squashed 'src/rocksdb/' content from commit 224932d

git-subtree-dir: src/rocksdb
git-subtree-split: 224932d4d0b561712107d747c662df181c39644d
Merge commit 'f86d9fd626df1cee55bce4c577d06bb064dc827b' as 'src/rocksdb'
Update rocksdb unity file (RIPD-352)
Refactor SField (RIPD-431)
* Restrict access to SField constructors.
* Make all SField access const.
* Hide and simplify databases used to hold SField constants.
* Separate the two concerns of representing a field,
  and maintaining a database of fields.