Remove MainWindow styleChanged() signal

There's no need to create multiple signals - connect() is fine with
connecting styleChanged(MainWindow::QGC_MAINWINDOW_STYLE)  to a slot
with no parameters.

src/ui/MainWindow.cc

@@ -1145,7 +1145,6 @@ bool MainWindow::loadStyle(QGC_MAINWINDOW_STYLE style, QString cssFile)
         // And trigger any changes to other UI elements that are watching for
         // theme changes.
         emit styleChanged(style);
-        emit styleChanged();
 
         // Finally restore the cursor before returning.
         qApp->restoreOverrideCursor();

src/ui/MainWindow.h

@@ -300,7 +300,6 @@ protected slots:
 
 signals:
     void styleChanged(MainWindow::QGC_MAINWINDOW_STYLE newTheme);
-    void styleChanged();
     void initStatusChanged(const QString& message, int alignment, const QColor &color);
 #ifdef MOUSE_ENABLED_LINUX
     /** @brief Forward X11Event to catch 3DMouse inputs */

src/ui/linechart/LinechartWidget.cc

@@ -138,7 +138,7 @@ LinechartWidget::LinechartWidget(int systemid, QWidget *parent) : QWidget(parent
     createLayout();
 
     // And make sure we're listening for future style changes
-    connect(MainWindow::instance(), SIGNAL(styleChanged()), this, SLOT(recolor()));
+    connect(MainWindow::instance(), SIGNAL(styleChanged(MainWindow::QGC_MAINWINDOW_STYLE)), this, SLOT(recolor()));
 
     updateTimer->setInterval(updateInterval);
     connect(updateTimer, SIGNAL(timeout()), this, SLOT(refresh()));