kv: less error tolerance in txn correctness tests
kv: less error tolerance in txn correctness tests

Removed the nondescript "expectError" boolean in the txn correctness tests. There
was only one test which relied on it (which was easily refactored).

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