util/cache: avoid panic when removing a list element twice
util/cache: avoid panic when removing a list element twice

This brings back the behavior that was present prior to #6140.

See #6190.

vivekmenezes/cockroach,sunya123/cockroach,cockroachdb/cockroach,paperstreet/cockroach,paperstreet/cockroach,sunya123/cockroach,veteranlu/cockroach,paperstreet/cockroach,sunya123/cockroach,sunya123/cockroach,maxlang/cockroach,petermattis/cockroach,sunya123/cockroach,sunya123/cockroach,vivekmenezes/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,glycerine/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,glycerine/cockroach,vivekmenezes/cockroach,arjun4084346/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,arjun4084346/cockroach,petermattis/cockroach,vivekmenezes/cockroach,petermattis/cockroach,arjun4084346/cockroach,maxlang/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,sunya123/cockroach,glycerine/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,paperstreet/cockroach,petermattis/cockroach,glycerine/cockroach,maxlang/cockroach,veteranlu/cockroach,maxlang/cockroach,paperstreet/cockroach,petermattis/cockroach,veteranlu/cockroach,arjun4084346/cockroach,paperstreet/cockroach,petermattis/cockroach,veteranlu/cockroach,vivekmenezes/cockroach,petermattis/cockroach,glycerine/cockroach,veteranlu/cockroach,vivekmenezes/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,maxlang/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,glycerine/cockroach,glycerine/cockroach,paperstreet/cockroach,vivekmenezes/cockroach,maxlang/cockroach,cockroachdb/cockroach,arjun4084346/cockroach,glycerine/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,maxlang/cockroach,arjun4084346/cockroach,petermattis/cockroach,sunya123/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,maxlang/cockroach