Revert "Adapt scheduler to work with dynamic derivations"

This reverts commit 5e3986f59c. This
un-implements RFC 92 but fixes the critical bug #9052 which many people
are hitting. This is a decent stop-gap until a minimal reproduction of
that bug is found and a proper fix can be made.

Mostly fixed #9052, but I would like to leave that issue open until we
have a regression test, so I can then properly fix the bug (unbreaking
RFC 92) later.

src/libstore/derived-path-map.hh

@@ -20,11 +20,8 @@ namespace nix {
  *
  * @param V A type to instantiate for each output. It should probably
  * should be an "optional" type so not every interior node has to have a
- * value. For example, the scheduler uses
- * `DerivedPathMap<std::weak_ptr<CreateDerivationAndRealiseGoal>>` to
- * remember which goals correspond to which outputs. `* const Something`
- * or `std::optional<Something>` would also be good choices for
- * "optional" types.
+ * value. `* const Something` or `std::optional<Something>` would be
+ * good choices for "optional" types.
  */
 template<typename V>
 struct DerivedPathMap {