Revert "add ir unknowninc instruction"

This reverts commit ebd62485df.

compiler/mono/src/expand_rc.rs

@@ -575,17 +575,6 @@ fn expand_and_cancel<'a>(env: &mut Env<'a, '_>, stmt: &'a Stmt<'a>) -> &'a Stmt<
                 expand_and_cancel(env, cont)
             }
 
-            Refcounting(
-                ModifyRc::IncUnknown {
-                    to_increment: _,
-                    amount: _,
-                },
-                cont,
-            ) => {
-                // TODO
-                expand_and_cancel(env, cont)
-            }
-
             Refcounting(ModifyRc::Inc(symbol, inc_amount), cont) => {
                 let count = env.deferred.inc_dec_map.entry(*symbol).or_insert(0);
                 *count += *inc_amount as i64;