Don't ignore an absent drv file in queryPartialDrvOutputMap

This ignore was here because `queryPartialDrvOutputMap` was used both
1. as a cache to avoid having to re-read the derivation (when gc-ing for
example), and
2. as the source of truth for ca realisations

The use-case 2. required it to be able to work even when the derivation
wasn't there anymore (see https://github.com/NixOS/nix/issues/4138).
However, this use-case is now handled by `queryRealisation`, meaning
that we can safely error out if the derivation isn't there anymore

src/libstore/local-store.cc

@@ -912,12 +912,7 @@ LocalStore::queryPartialDerivationOutputMap(const StorePath& path_)
         auto state(_state.lock());
         std::map<std::string, std::optional<StorePath>> outputs;
         uint64_t drvId;
-        try {
         drvId = queryValidPathId(*state, path);
-        } catch (InvalidPath&) {
-            // Ignore non-existing drvs as they might still have an output map
-            // defined if ca-derivations is enabled
-        }
         auto use(state->stmts->QueryDerivationOutputs.use()(drvId));
         while (use.next())
             outputs.insert_or_assign(