Revert "Rollup merge of #149147 - chenyukang:yukang-fix-unused_assignments-macro-gen-147648, r=JonathanBrouwer"

This reverts commit 82a17b3, reversing
changes made to 5019bda.

Author: Kobzol

compiler/rustc_mir_transform/src/liveness.rs

@@ -75,11 +75,6 @@ pub(crate) fn check_liveness<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Den
         return DenseBitSet::new_empty(0);
     }
 
-    // Don't run unused pass for items generated by foreign macros
-    if tcx.def_span(parent).in_external_macro(tcx.sess.source_map()) {
-        return DenseBitSet::new_empty(0);
-    }
-
     let mut body = &*tcx.mir_promoted(def_id).0.borrow();
     let mut body_mem;