Best way to quickly and effectively drop a database and delete all files?

Unless you are in the context of the database, you can't ensure you are the only one using it. Also, don't use batch separators. Run it all as a single batch.

Use AlwaysEncryptedSample;

ALTER DATABASE AlwaysEncryptedSample SET SINGLE_USER WITH ROLLBACK IMMEDIATE;

Use master;

DROP DATABASE AlwaysEncryptedSample;

I use the following sequence:

1. Switch to master (or tempdb or any other database besides the one I want to drop)
2. Force the database offline
3. Set it online

4. Drop the database:

   USE master;
   GO
   ALTER DATABASE AlwaysEncryptedSample 
       SET OFFLINE WITH ROLLBACK IMMEDIATE;
   GO
   ALTER DATABASE AlwaysEncryptedSample SET ONLINE;
   GO
   DROP DATABASE AlwaysEncryptedSample;
   GO
   

The problem is if some process is constantly attaching to that database, it becomes a race condition and might not work.