[krbdev.mit.edu #6299] krb5_stdccv3_remove mem leak

[Greg Hudson via RT]

This patch appears to blow away the value of err from the loop.  If, for
instance, the specified credential is not found, the function would
probably return successfully anyway because it was able to release the
iterator.

Also, if credentials were successfully removed but the iterator could
not be released, cache_changed() should probably still be called.