The filterclear message tells the receiving peer to remove a previously-set bloom filter.
Part of the connection bloom filtering mechanism as described in BIP-37.
This also undoes the effect of setting the relay field in the “version” message to 0, allowing unfiltered access to “inv” messages announcing new transactions.
unit-e does not require a “filterclear” message before a replacement filter is loaded with a “filterload” message. It also doesn’t require a “filterload” message before a “filterclear” message.
There is no payload in a “filterclear” message. See the message header section for an example of a message without a payload.