rust: remove unused error variant

rust: remove unused error variant

All paths check that the working directory revision is not used.

--- a/rust/hg-core/src/revlog/mod.rs	Mon Aug 07 12:53:43 2023 +0200
+++ b/rust/hg-core/src/revlog/mod.rs	Mon Aug 07 15:07:48 2023 +0200
@@ -76,7 +76,6 @@
 #[derive(Clone, Debug, PartialEq)]
 pub enum GraphError {
     ParentOutOfRange(Revision),
-    WorkingDirectoryUnsupported,
 }
 
 /// The Mercurial Revlog Index

--- a/rust/hg-cpython/src/cindex.rs	Mon Aug 07 12:53:43 2023 +0200
+++ b/rust/hg-cpython/src/cindex.rs	Mon Aug 07 15:07:48 2023 +0200
@@ -15,7 +15,7 @@
     PyObject, PyResult, PyTuple, Python, PythonObject,
 };
 use hg::revlog::{Node, RevlogIndex};
-use hg::{Graph, GraphError, Revision, WORKING_DIRECTORY_REVISION};
+use hg::{Graph, GraphError, Revision};
 use libc::{c_int, ssize_t};
 
 const REVLOG_CABI_VERSION: c_int = 3;
@@ -141,9 +141,6 @@
 impl Graph for Index {
     /// wrap a call to the C extern parents function
     fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
-        if rev == WORKING_DIRECTORY_REVISION {
-            return Err(GraphError::WorkingDirectoryUnsupported);
-        }
         let mut res: [c_int; 2] = [0; 2];
         let code = unsafe {
             (self.capi.index_parents)(
@@ -170,9 +167,6 @@
             Err(GraphError::ParentOutOfRange(rev)) => {
                 Err(vcsgraph::graph::GraphReadError::KeyedInvalidKey(rev))
             }
-            Err(GraphError::WorkingDirectoryUnsupported) => Err(
-                vcsgraph::graph::GraphReadError::WorkingDirectoryUnsupported,
-            ),
         }
     }
 }

--- a/rust/hg-cpython/src/exceptions.rs	Mon Aug 07 12:53:43 2023 +0200
+++ b/rust/hg-cpython/src/exceptions.rs	Mon Aug 07 15:07:48 2023 +0200
@@ -26,15 +26,6 @@
             hg::GraphError::ParentOutOfRange(r) => {
                 GraphError::new(py, ("ParentOutOfRange", r))
             }
-            hg::GraphError::WorkingDirectoryUnsupported => {
-                match py
-                    .import("mercurial.error")
-                    .and_then(|m| m.get(py, "WdirUnsupported"))
-                {
-                    Err(e) => e,
-                    Ok(cls) => PyErr::from_instance(py, cls),
-                }
-            }
         }
     }