pub fn remove_entry_mult(self) -> (MetadataKey<VE>, ValueDrain<'a, VE>) {
        let (name, value_drain) = self.inner.remove_entry_mult();
        (
            MetadataKey::unchecked_from_header_name(name),
            ValueDrain {
                inner: value_drain,
                phantom: PhantomData,
            },
        )
    }
Remove the entry from the map.

The key and all values associated with the entry are removed and
returned.
tonic/src/metadata/map.rs