robot_interface_streaming.launch prevents pushing down namespace

[BrettHemes]

The leading forward slashes in robot_interface_streaming.launch are problematic when trying to put (push down) the eki driver within a different namespace.

Removing them seems to fix the problem (see PR #144)
@gavanderhoorn I believe I remember you saying these files were strictly for convenience and would probably get changed/deleted/improved? Regardless I just wanted to point out that we are using this modification in our current use cases.