Revert "simplCore: Correctly extend in-scope set in rule matching"

This reverts commit 8bbdba45.

compiler/GHC/Core/Rules.hs

@@ -955,7 +955,7 @@ match renv subst e1 (Let bind e2) mco
   | otherwise
   = Nothing
   where
-    (flt_subst', bind') = substBind (rv_fltR renv `extendInScopeList` rs_bndrs subst) bind
+    (flt_subst', bind') = substBind (rv_fltR renv) bind
     new_bndrs           = bindersOf bind'
 
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