bugfix: don't try to delete a parameter that doesn't exist
bugfix: don't try to delete a parameter that doesn't exist

(cherry-picked from 2.5: 9112b933a1bb2ed04dd18024ed8273b1ea2e0f2a)

Ensembl/ensembl-hive,Ensembl/ensembl-hive,Ensembl/ensembl-hive,Ensembl/ensembl-hive