Now simply inherits attrsets from super directly instead of mapping getAttr over
a list of strings.
Filtering isn't really needed as non-existent subsets should just be removed
from this list when removing them from Nixpkgs (such an action warrants a
tree-wide search which should come across this file).
recurseIntoAttrs can simply be mapAttr'd now.
Some subsets have been removed because they no longer exist.
Sorted the list while I was at it.
