[IR] Remove an unnecessary cast (NFC) (#146250)

Agg is already of Type *.

Author: kazutakahirata

llvm/lib/IR/Instructions.cpp

@@ -2582,7 +2582,7 @@ Type *ExtractValueInst::getIndexedType(Type *Agg,
       return nullptr;
     }
   }
-  return const_cast<Type*>(Agg);
+  return Agg;
 }
 
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