all-packages.nix: Alias self to res, deprecating self

For historical reasons, self was ill-named. This removes its usages
from all-packages.nix and provides a deprecation message for those
who use a patched Nixpkgs.

Some packages seem to depend on the peculiarities of res, as can
be seen by making res into an alias of pkgs (normally "self").
The super variable doesn't have all that is needed.

Therefore the simple fix is not guaranteed to work and as such,
usages of res need to be changed to pkgs or super, case by case.