Remove workaround for handling missing `PUT_VALUE` ACKs

[dmitry-markin]

Due to litep2p not previously implementing PUT_VALUE ACK messages, #430 implements a hackish way of dealing with such older nodes. It does two things:

1. Tracks PUT_VALUE send successes instead of ACK responses to determine the query success.
2. Ignores send errors when the remote doesn't read the PUT_VALUE ACK message.

Once most of the network is on a newer litep2p version, this hackish implementation must be replaced with a proper PUT_VALUE ACK handling.