Squash minor warning in vm/mod.rs

Inst::Comment is no longer printing, so we don't need the "comment"
variable to be usable.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/vm/mod.rs

@@ -236,7 +236,7 @@ impl Vm {
                 );
                 self.set_condition(top.is_truthy());
             }
-            Inst::Comment(comment) => {
+            Inst::Comment(_comment) => {
                 /* no-op */
                 //println!("COMMENT: {comment}");
             }