Fix: when pressing 'delete me', all contents of parent directory are deleted.

Changed 'delete' switch case so to only delete a single file (if running
compiled-file version) or to delete a few named files (if running from a
directory of uncompressed files). That avoids deleting complete
WordPress site if script is running from a root directory.
Avoided warning 'Strict Standards: Only variables should be passed by reference' when pressing 'delete me'