refactor(tvix/eval) remove Value::DynamicUpvalueMissing

I believe this variant is left over from a previous implementation.
If not, please let me know.

Signed-off-by: Adam Joseph <adam@westernsemico.com>
Change-Id: I02a3bf2f63794d09e96a5a92a034c0ad3d1ff221
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7027
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/eval/src/vm.rs

@@ -836,10 +836,7 @@ impl<'o> VM<'o> {
 
             // If any of these internal values are encountered here a
             // critical error has happened (likely a compiler bug).
-            Value::AttrNotFound
-            | Value::DynamicUpvalueMissing(_)
-            | Value::Blueprint(_)
-            | Value::DeferredUpvalue(_) => {
+            Value::AttrNotFound | Value::Blueprint(_) | Value::DeferredUpvalue(_) => {
                 panic!("tvix bug: internal value left on stack: {:?}", value)
             }