Archivelog file deleted, resulting in 'ORA-01113: file 1 needs media recovery'
Ran an RMAN archivelog backup to a new directory
  Changed my mind and deleted that directory.


Assuming you still have the archivelog files and they were not deleted when they were backed up, you just need to tell RMAN that those files aren't coming back:


  Use the CROSSCHECK command to synchronize the physical reality of backups and copies with their logical records in the RMAN repository


If, on the other hand, the original archivelog files were deleted along with their backups, you do not have a full recovery set and it is a good thing you said "This is not a production database. I'm practising in a staging environment". A full backup run online is not a consistent backup — you need the archivelog files containing log records from just before the backup starts until just after it finishes or there is no way to restore the database consistently.