kv: Avoid intermediate slice when adding intents to txnMetadata
kv: Avoid intermediate slice when adding intents to txnMetadata

This removed a TODO.

arjun4084346/cockroach,bg451/cockroach,vaibhavarora/cockroach,sunya123/cockroach,sunya123/cockroach,maxlang/cockroach,veteranlu/cockroach,glycerine/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,cockroachdb/cockroach,sunya123/cockroach,cockroachdb/cockroach,paperstreet/cockroach,paperstreet/cockroach,paperstreet/cockroach,maxlang/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,maxlang/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,cockroachdb/cockroach,petermattis/cockroach,arjun4084346/cockroach,vivekmenezes/cockroach,petermattis/cockroach,veteranlu/cockroach,paperstreet/cockroach,sunya123/cockroach,petermattis/cockroach,vivekmenezes/cockroach,bg451/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,bg451/cockroach,vaibhavarora/cockroach,glycerine/cockroach,arjun4084346/cockroach,sunya123/cockroach,maxlang/cockroach,maxlang/cockroach,bg451/cockroach,arjun4084346/cockroach,arjun4084346/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,sunya123/cockroach,vaibhavarora/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,arjun4084346/cockroach,veteranlu/cockroach,cockroachdb/cockroach,veteranlu/cockroach,glycerine/cockroach,petermattis/cockroach,glycerine/cockroach,maxlang/cockroach,vaibhavarora/cockroach,glycerine/cockroach,sunya123/cockroach,vaibhavarora/cockroach,bg451/cockroach,arjun4084346/cockroach,maxlang/cockroach,arjun4084346/cockroach,paperstreet/cockroach,petermattis/cockroach,petermattis/cockroach,sunya123/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,paperstreet/cockroach,bg451/cockroach,glycerine/cockroach,bg451/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,petermattis/cockroach,glycerine/cockroach,glycerine/cockroach,petermattis/cockroach,maxlang/cockroach