Unable to remove additional tempdb file
So your current situation is a full drive where you have two TempDB's that you want to modify the old one's size and the newly created one is having difficulties being removed?


  There are limitations for use of the DBCC SHRINKDATABASE command on
  the tempdb database. The target size for data and log files cannot be
  smaller than the size that is specified when the database was created
  or smaller than the last size that was explicitly set by using a
  file-size-changing operation such as ALTER DATABASE that uses the
  MODIFY FILE option or the command. Another limitation of BCC
  SHRINKDATABASE is the calculation of the target_percentage parameter
  and its dependency on the current space that is used.


Try running:

dbcc shrinkdatabase (tempddev, '70') 


This should set your file to ~54GB which should be a safe size considering I am assuming your size or model was 30GB. Adjust the % accordingly.

Microsoft - How to shrink tempdb

Now for the second file, give this a try:

USE [tempdb]
GO
DBCC SHRINKFILE (N'tempdev2', EMPTYFILE)
GO

USE [tempdb]
GO
ALTER DATABASE [tempdb] REMOVE FILE [tempdev2]
GO


If the issue persists, you'll have to restart SQL Server to remove the file as TempDB is in use.

Microsoft Forum - File in use

SQL Authority - Shrink and remove Tempdb file

One last note, you typed this:


  ALTER DATABASE tempdb
  ADD FILE (NAME='tempdev2', FILENAME='M:\SQLData**tempdb3**.ndf', Size=30GB);


Your screenshot shows tempdb2, make sure your accurate with all the names and double check them. Just in case there is a mistype and that is causing your headaches. 

There are some cases where running

DBCC FREEPROCCACHE


can help alleviate the pain and allow you to shrink the file.

Ozar - When TempDB won't shrink.

If you are still having issues, see what is out in your tempdb:

select * from tempdb.sys.all_objects
where is_ms_shipped = 0;


This will let you see your size of the tempdb files. 

USE [tempdb]
SELECT
   [name]
   ,CONVERT(NUMERIC(10,2),ROUND([size]/128.,2))                                 AS [Size]
   ,CONVERT(NUMERIC(10,2),ROUND(FILEPROPERTY([name],'SpaceUsed')/128.,2))            AS [Used]
   ,CONVERT(NUMERIC(10,2),ROUND(([size]-FILEPROPERTY([name],'SpaceUsed'))/128.,2))      AS [Unused]
FROM [sys].[database_files]


From your post we see that you have files used in TempDB and there is space free. SQLSunday by Daniel Hutmacher has a good link on shrinking your DB with additional methods that were similar to Ozar, I would recommend to give this a try as well with caution.

There is a post by Mike Good - SQL Central on shrinking your TempDB by adjusting the snapshot level of TempDB with a rollback period to kill any connections that may have lingered on your db.