locks: remove dead lease error-handling code

A minor oversight from f7347ce4ee7c65415f84be915c018473e7076f31,
"fasync: re-organize fasync entry insertion to allow it under a
spinlock": this cleanup-on-error was only needed to handle -ENOMEM.  Now
that we're preallocating it's unneeded.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>