You can't delete any log file that has any portion of the active log regardless of whether there are any currently running transactions or not (stopping transactions won't change that).
Use DBCC LOGINFO to identify which file the active portion of the log is in (VLFs with a status of 2), when all of those are in one file, you can drop the other with an ALTER DATABASE statement.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability