[clang-tidy] remove pointless void arg

Found with modernize-redundant-void-arg

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/output/State.cxx

@@ -80,7 +80,7 @@ audio_output_state_read(const char *line, MultipleOutputs &outputs)
 }
 
 unsigned
-audio_output_state_get_version(void)
+audio_output_state_get_version()
 {
 	return audio_output_state_version;
 }

src/output/plugins/JackOutputPlugin.cxx

@@ -419,7 +419,7 @@ JackOutput::Connect()
 }
 
 static bool
-mpd_jack_test_default_device(void)
+mpd_jack_test_default_device()
 {
 	return true;
 }

src/output/plugins/PulseOutputPlugin.cxx

@@ -872,7 +872,7 @@ try {
 }
 
 static bool
-pulse_output_test_default_device(void)
+pulse_output_test_default_device()
 {
 	return PulseOutput::TestDefaultDevice();
 }