refactor(tvix/eval): remove OpResolveWithOrUpvalue

The case branch in vm.rs for OpResolveWithOrUpvalue is
unreachable/deadcode.

I believe this opcode is unnecessary, since it should always be
statically detectable (at parse-time) whether a reference is to an
upvalue (i.e. enclosing binding); otherwise, and only then, is
with-resolution applicable.

Perhaps I've misunderstood how with-resolution works.  If so, please
explain it to me and -1/-2 this CL.

Signed-off-by: Adam Joseph <adam@westernsemico.com>
Change-Id: I4a90b9eb6cb3396df92a6a943d42ecc301871ba0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7009
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/eval/src/opcode.rs

@@ -100,7 +100,6 @@ pub enum OpCode {
     OpPushWith(StackIdx),
     OpPopWith,
     OpResolveWith,
-    OpResolveWithOrUpvalue(UpvalueIdx),
 
     // Lists
     OpList(Count),