Fix multiple definition error.

I f'ed up the merge.

src/Platform/GlxApplication.h

@@ -82,8 +82,6 @@ class GlxApplication: public AbstractXApplication {
         ~GlxApplication();
 };
 
-GlxApplication::~GlxApplication() = default;
-
 /** @hideinitializer
 @brief Entry point for GLX-based applications
 @param className Class name

src/Platform/XEglApplication.h

@@ -83,8 +83,6 @@ class XEglApplication: public AbstractXApplication {
         ~XEglApplication();
 };
 
-XEglApplication::~XEglApplication() = default;
-
 /** @hideinitializer
 @brief Entry point for X/EGL-based applications
 @param className Class name