This MSDN article describes how to accomplish this at a high-level:
You cannot move transaction log data from one log file to another to
empty a transaction log file. To remove inactive transactions from a
transaction log file, the transaction log must be truncated or backed
up. When the transaction log file no longer contains any active or
inactive transactions, the log file can be removed from the database.
And this blog post shows the actual T-SQL that will accomplish this task:
USE master
IF DB_ID('rDb') IS NOT NULL DROP DATABASE rDb
GO
CREATE DATABASE rDb
ON
PRIMARY
( NAME = N'rDb', FILENAME = N'C:\rDb.mdf' , SIZE = 50MB ,
FILEGROWTH = 1024KB )
LOG ON
(NAME = N'rDb_log2', FILENAME = N'C:\rDb_log2.ldf', SIZE = 3MB,
FILEGROWTH = 2MB)
,(NAME = N'rDb_log3', FILENAME = N'C:\rDb_log3.ldf', SIZE = 3MB,
FILEGROWTH = 2MB)
,(NAME = N'rDb_log4', FILENAME = N'C:\rDb_log4.ldf', SIZE = 3MB,
FILEGROWTH = 2MB)
GO
ALTER DATABASE rDb SET RECOVERY FULL
BACKUP DATABASE rDb TO DISK = 'C:\rDb.bak' WITH INIT
CREATE TABLE rDb..t(c1 INT IDENTITY, c2 CHAR(100))
INSERT INTO rDb..t
SELECT TOP(15000) 'hello'
FROM syscolumns AS a
CROSS JOIN syscolumns AS b
--Log is now about 46% full
DBCC SQLPERF(logspace)
--Check virtual log file layout
DBCC LOGINFO(rDb)
--See that file 4 isn't used at all (Status = 0 for all 4's rows)
--We can remove file 4, it isn't used
ALTER DATABASE rDb REMOVE FILE rDb_log4
--Check virtual log file layout
DBCC LOGINFO(rDb)
--Can't remove 3 since it is in use
ALTER DATABASE rDb REMOVE FILE rDb_log3
--What if we backup log?
BACKUP LOG rDb TO DISK = 'C:\rDb.bak'
--Check virtual log file layout
DBCC LOGINFO(rDb)
--3 is still in use (status = 2)
--Can't remove 3 since it is in use
ALTER DATABASE rDb REMOVE FILE rDb_log3
--Shrink 3
USE rDb
DBCC SHRINKFILE(rDb_log3)
USE master
--... and backup log?
BACKUP LOG rDb TO DISK = 'C:\rDb.bak'
--Check virtual log file layout
DBCC LOGINFO(rDb)
--3 is no longer in use
--Can now remove 3 since it is not in use
ALTER DATABASE rDb REMOVE FILE rDb_log3
--Check explorer, we're down to 1 log file
--See what sys.database_files say?
SELECT * FROM rDb.sys.database_files
--Seems physical file is gone, but SQL Server consider the file offline
--Backup log does it:
BACKUP LOG rDb TO DISK = 'C:\rDb.bak'
SELECT * FROM rDb.sys.database_files
--Can never remove the first ("primary") log file
ALTER DATABASE rDb REMOVE FILE rDb_log2
--Note error message from above