Force TTS to English (on Linux only)

Remove unnecessary AudioOutput dependencies.

src/Audio/AudioOutput.cc

@@ -20,14 +20,12 @@ AudioOutput::AudioOutput(QGCApplication* app, QGCToolbox* toolbox)
     : QGCTool(app, toolbox)
     , _tts(new QTextToSpeech(this))
 {
-    _tts->setLocale(QLocale::system());
+    //-- Force TTS engine to English as all incoming messages from the autopilot
+    //   are in English and not localized.
+#ifdef Q_OS_LINUX
+    _tts->setLocale(QLocale("en_US"));
+#endif
     connect(_tts, &QTextToSpeech::stateChanged, this, &AudioOutput::_stateChanged);
-    connect(qgcApp(), &QGCApplication::languageChanged, this, &AudioOutput::_languageChanged);
-}
-
-void AudioOutput::_languageChanged(const QLocale locale)
-{
-    _tts->setLocale(locale);
 }
 
 bool AudioOutput::say(const QString& inText)

src/Audio/AudioOutput.h

@@ -33,7 +33,6 @@ public slots:
 
 private slots:
     void            _stateChanged           (QTextToSpeech::State state);
-    void            _languageChanged        (const QLocale locale);
 
 protected:
     QTextToSpeech*  _tts;

src/QGCApplication.cc

@@ -42,7 +42,6 @@
 
 #include "QGC.h"
 #include "QGCApplication.h"
-#include "AudioOutput.h"
 #include "CmdLineOptParser.h"
 #include "UDPLink.h"
 #include "LinkManager.h"

src/Vehicle/Vehicle.cc

@@ -28,7 +28,6 @@
 #include "ParameterManager.h"
 #include "QGCApplication.h"
 #include "QGCImageProvider.h"
-#include "AudioOutput.h"
 #include "FollowMe.h"
 #include "MissionCommandTree.h"
 #include "QGroundControlQmlGlobal.h"

src/uas/UAS.cc

@@ -26,7 +26,6 @@
 #include "UAS.h"
 #include "LinkInterface.h"
 #include "QGC.h"
-#include "AudioOutput.h"
 #include "MAVLinkProtocol.h"
 #include "QGCMAVLink.h"
 #include "LinkManager.h"