uv-resolver: remove code that was intended to be removed

In particular, I added this as a hack to avoid a kinda of
instability that was caused by our marker code not correctly
detecting markers that were always false. But that has since
been fixed.

Removing this code doesn't change any tests. Arguably it
should be possible to come up with a test that failed with
this hack inserted but succeeded without it. In particular,
with this hack, new forks were being prevented from being
added even when they ought to be added, e.g., when preferences
get updated.

crates/uv-resolver/src/resolver/mod.rs

@@ -1431,29 +1431,6 @@ impl<InstalledPackages: InstalledPackagesProvider> ResolverState<InstalledPackag
                 ))
             }
         };
-
-        // At present, if we know that we are running resolution
-        // starting with an existing set of forks, then we
-        // explicitly and forcefully prevent any new forks from
-        // being created. The motivation for doing this is that our
-        // `is_definitively_empty_set` logic for detecting whether
-        // a marker expression matches the empty set isn't yet
-        // bullet proof. Moreover, when re-running resolution, it's
-        // possible for new forks to get generated that ultimately are
-        // superfluous due to empty set markers. While we do filter
-        // these out, we do it via `is_definitively_empty_set`.
-        //
-        // Ideally we wouldn't do this here forcefully since if
-        // the input requirements change (i.e., `pyproject.toml`),
-        // then it could be correct to introduce a new fork.
-        // But in order to remove this, I think we need to make
-        // `is_definitively_empty_set` better than it is today.
-        if let ResolverMarkers::Universal { fork_preferences } = markers {
-            if !fork_preferences.is_empty() {
-                return Ok(Dependencies::Unforkable(dependencies));
-            }
-        }
-
         Ok(Dependencies::Available(dependencies))
     }