### METADATA CLEAR

This subcommand MUST remove all metadata, equivalently to using `METADATA SET`
on all currently-set keys with an empty value. The format of `METADATA CLEAR`
MUST be as follows:

`METADATA <Target> CLEAR`

The server MUST respond with one `RPL_KEYVALUE` event per cleared key and one
`RPL_METADATAEND` event.

Servers MAY omit certain metadata, which is considered not visible for
the requesting user, or replace it with `ERR_KEYNOPERMISSION`.

It is an error for users to use this subcommand on targets for which they lack
authorization from the server. Servers MAY reject this subcommand for channels,
using `ERR_KEYNOPERMISSION` with an asterisk (`*`) in the `<Key>` field.