steam-runtime-tools: Separate out modules not in the shared library
We don't need to link SrtPortalListener or SrtPtyBridge into the shared library, only into the executable utilities.
This is in preparation for maybe moving more of the pressure-vessel code into steam-runtime-tools/
where we can easily use it from bin/
. In particular, steamrt/tasks#387 could benefit from having a locking "adverb" utility in scout that is rather similar to pressure-vessel-adverb
.