Rename x11 auto-type plugin to xcb.

This matches what QGuiApplication::platformName() returns.

src/core/Tools.cpp

@@ -17,7 +17,7 @@
 
 #include "Tools.h"
 
-#include <QApplication>
+#include <QCoreApplication>
 #include <QImageReader>
 #include <QIODevice>
 #include <QLocale>
@@ -192,26 +192,6 @@ void wait(int ms)
     }
 }
 
-QString platform()
-{
-    // TODO: move callers to QApplication::platformName()
-
-    QString platform = QApplication::platformName();
-
-    if (platform == "xcb") {
-        return "x11";
-    }
-    else if (platform == "cocoa") {
-        return "mac";
-    }
-    else if (platform == "windows") {
-        return "win";
-    }
-    else {
-        return platform;
-    }
-}
-
 void disableCoreDumps()
 {
     // default to true

src/core/Tools.h

@@ -36,7 +36,6 @@ QString imageReaderFilter();
 bool isHex(const QByteArray& ba);
 void sleep(int ms);
 void wait(int ms);
-QString platform();
 void disableCoreDumps();
 
 } // namespace Tools