mds: eval stray on remove dentry replica

mds: eval stray on remove dentry replica

This happens because when handling an MCacheExpire,
we expire inodes first and then dentries, so when
the inodes are put() their dentries still are replicated
so eval_stray fails.  Do an explicit call to maybe_eval_stray
when handling the expire for the dentry in order to catch
this.

One hits this path when migrating a stray away from
a stopping MDS rank.

Signed-off-by: John Spray <john.spray@redhat.com>