Transport: Remove parsing of port ranges

UnicastZenDiscovery allowed you to specify port ranges for hosts to connect to.
However only the first port was used at all, when specifying something like
`host[9300-9400]`. This commit only accepts `host:port` pairs and thus makes
the configuration reflect the execution as even in the old setup only a single
host:port pair was pinged at all, as this was very expensive.

Note there is a coming PR for 1.x, which deprecates this setting and emits a warning instead of removing it.
I am confused here. This is not about binding to a port when starting, only about connecting to other nodes, as far as I can judge the source codes. Starting up several nodes in parallel on one machines still works as expected