They are not doing anything right now. This is in preparation for their
complete removal from the tree.
Note: several changes that affect the derivation inputs (e.g. removal of
references to stub paths in build instructions) were left out. They will
be cleaned up the next iteration and will require special care.
Note: this PR is a result of a mix of ugly regex (not AST) based
automation and some manual labor. For reference, the regex automation
part was hacked in: https://github.com/booxter/nix-clean-apple_sdk
Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>