Android: Remove unused functions

As found by Cppcheck

Change-Id: I9274fe45ed49099b52b4f8556508ec0adc676386
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

src/plugins/android/androidsdkmanager.h

@@ -67,7 +67,6 @@ public:
 
     SdkPlatformList installedSdkPlatforms();
     const AndroidSdkPackageList &allSdkPackages();
-    AndroidSdkPackageList availableSdkPackages();
     AndroidSdkPackageList installedSdkPackages();
     SystemImageList installedSystemImages();
     NdkList installedNdkPackages();