storage: remove TODO about locking
storage: remove TODO about locking

This was substantially refactored in #7085.

Closes #4562.

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