Stub out `pa_start_child_for_read`.
As far as I can tell, the main suspect call is
pa_start_child_for_read() in libpulsecore. As far as I can tell:
- The only consumer appears to be the
gconfmodule, which is hardcoded to execute
- Despite what the Tails bugs says, this does not appear to directly be exposed to any IPC calls.
gconf doesn't exist inside the sandbox this should be harmless, but I might as well stub it out anyway.