Review channel version code and cleanup

[ancazamfir]

Summary of Bug

We should cleanup the code around channel version according to the changes in cosmos/ibc#628

Version

Steps to Reproduce

Acceptance Criteria

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[seanchen1991]

@ancazamfir could you clarify what changes need to occur in Hermes in order to satisfy the changes proposed in cosmos/ibc#628?

[romac]

@seanchen1991 For open init, I think it's just a matter of turning this

hermes/crates/relayer/src/channel.rs

Lines 838 to 854 in a69bf5c

	// If the user supplied a version, use that.
	// Otherwise, either use the version defined for the `transfer`
	// or an empty version if the port is non-standard.
	let version = self
	.dst_version()
	.cloned()
	.or_else(|| version::default_by_port(self.dst_port_id()))
	.unwrap_or_else(|| {
	warn!(
	chain = %self.dst_chain().id(),
	channel = ?self.dst_channel_id(),
	port = %self.dst_port_id(),
	"no version specified for the channel, falling back on empty version"
	);
	Version::empty()
	});

into something like this

        // If the user supplied a version, use that.
        // Otherwise, use the empty version and let the app decide on it.
        let version = self.dst_version().cloned().unwrap_or_else(Version::empty);

And remove default_by_port.

[romac]

For open try, we already use the version that the app decided on, so there is nothing to do here.

hermes/crates/relayer/src/channel.rs

Lines 1023 to 1024 in a69bf5c

	// Re-use the version that was either set on ChanOpenInit or overwritten by the application.
	let version = src_channel.version().clone();

We could pass the empty version here since the app is going to ignore it anyway, but I don't believe it's necessary.

[seanchen1991]

Closing this as it seems like most chains have not incorporated these changes yet, so they aren't quite relevant for now. We can revisit if/when these changes become necessary.