Removing secondary data files. DBCC SHRINKFILE: Page could not be moved because it is a work table page
Restarting the server should be enough - those worktables should clear out. But I'd probably start it up in single user mode (-m) to prevent other processes from creating worktables before you successfully remove those files. Then redefine the files required for tempdb; perhaps deleting unnecessary files, changing sizes, etc. You should also ensure you have an even number of files, that they're all set to the same size, and that they all have the same autogrowth settings (in MB, not %). And it might be a good time to consider TF 1117 and TF 1118 as well (starting point).

I'd be very wary about the suggestion to just delete the files from the file system before starting SQL Server again - it might not start at all. 

(I'd also be curious about what the actual problem is, though. Having too many files doesn't hurt you, really.)