x11: Don't unload libGL.so to prevent a crash in XCloseDisplay()

libGL.so may register callbacks that can be invoked upon XCloseDisplay().
If XCloseDisplay() is called after libGL.so is unloaded, the callback pointer
will point at freed memory and invoking it will crash.

The texture framebuffer check optimized out in f37e4a9 was causing libGL.so to
never be unloaded as a side-effect. Skipping it exposed this bug by allowing
libGL.so to actually unload.

src/video/x11/SDL_x11opengl.c

@@ -247,11 +247,6 @@ X11_GL_LoadLibrary(_THIS, const char *path)
         X11_GL_UseEGL(_this) ) {
 #if SDL_VIDEO_OPENGL_EGL
         X11_GL_UnloadLibrary(_this);
-        /* Better avoid conflicts! */
-        if (_this->gl_config.dll_handle != NULL ) {
-            GL_UnloadObject(_this->gl_config.dll_handle);
-            _this->gl_config.dll_handle = NULL;
-        }
         _this->GL_LoadLibrary = X11_GLES_LoadLibrary;
         _this->GL_GetProcAddress = X11_GLES_GetProcAddress;
         _this->GL_UnloadLibrary = X11_GLES_UnloadLibrary;