Remove the dpipes replace directive

[jpc]

The go install tool complains about the replace directive in go.mod:

# go install github.com/webdataset/tarp/tarp@latest
go: downloading github.com/webdataset/tarp v0.0.2
go: downloading github.com/webdataset/tarp/tarp v0.0.0-20221009163818-4aac5677b928
go: github.com/webdataset/tarp/tarp@latest (in github.com/webdataset/tarp/tarp@v0.0.0-20221009163818-4aac5677b928):
	The go.mod file for the module providing named packages contains one or
	more replace directives. It must not contain directives that would cause
	it to be interpreted differently than if it were the main module.

After removing the directive the tool compiles and installs successfully. You can try this here: go install github.com/collabora/tarp/tarp@latest

Unfortunately the dependency on C libraries libzmq and libsodium still make it a lot more difficult to install on random machines (in clusters, docker containers etc.) than the old tarproc but unfortunately that seems a lot more difficult to fix. :)

[jpc]

Hey, I think it would be nice to merge this to make the tool a bit easier to install for people?