This commit removes an assertion which is not needed because with etcd
we can safely create keys and values with the same key since they are
stored under different keys in the DB. This saves us one unnecessary Get
on every Put.
The etcd cursor Delete stepped to the next item in the range before
Delete to not invalidate the iteation. This is unnecessary and not
compatible with bbolt, resulting in an extra fetch too.
From bbolt docs:
// Seek positions the cursor at the passed seek key. If the key does not exist,
// the cursor is moved to the next key after seek. Returns the new pair.
