This old config option was not plumbed though anymore because we stopped
supported snapshot builds where this was used. Nodepool doesn't want to
manage keypairs at all so no creation/addition/listing/deletion, instead
it now accepts per label key name for precreated key in cloud regions
and will boot with that. Unfortunately this old code was "cleaning" up
this new label specified key for us as the only thing it did anymore.
Fix this by removing the dead code and stop deleting keys it doesn't
know about as we aren't managing keys anymore.
Change-Id: Ifff93de1ad81315141bfe1a53dc3d8578faee8e6
7086877f0c