Do not implicitly prime VPIO when creating any duplex stream

The mere existance of VPIO may have side effects. For instance having
VPIO's input side hooked up to the builtin mic of my M2 Macbook Pro
causes a non-VPIO audio unit on the same device to expose three channels
(instead of 1) containing some very-low-volume audio.

With priming, when a client requests a non-VPIO duplex stream using the
builtin mic, it will therefore always get very-low-volume audio.

Having multiple VPIO units on this mic is fine.

src/backend/mod.rs

@@ -3032,10 +3032,6 @@ impl<'ctx> CoreStreamData<'ctx> {
         shared_voice_processing_unit: &mut SharedVoiceProcessingUnit,
     ) -> Result<(device_info, device_info)> {
         self.debug_assert_is_on_stream_queue();
-        if self.has_input() && self.has_output() {
-            shared_voice_processing_unit.prime();
-        }
-
         let should_use_voice_processing_unit = self.has_input()
             && self.has_output()
             && self