Remove deprecated constant.

islandora.module

@@ -61,9 +61,6 @@ define('ISLANDORA_DATASTREAM_INGESTED_HOOK', 'islandora_datastream_ingested');
 define('ISLANDORA_DATASTREAM_MODIFIED_HOOK', 'islandora_datastream_modified');
 define('ISLANDORA_DATASTREAM_PURGED_HOOK', 'islandora_datastream_purged');
 define('ISLANDORA_INGEST_STEP_HOOK', 'islandora_ingest_steps');
-// The "ISLANDORA_DERVIATIVE_CREATION_HOOK" constant has deprecated as of
-// 7.x-1.5, and should be removed after the next release.
-define('ISLANDORA_DERVIATIVE_CREATION_HOOK', 'islandora_derivative');
 define('ISLANDORA_DERIVATIVE_CREATION_HOOK', 'islandora_derivative');
 
 // Autocomplete paths.