EGL: move disconnect to surface dtor

This change moves the call to native_window_api_disconnect from
eglDestroySurface to the egl_surface_t destructor.  The egl_surface_t
can outlive the external EGLSurface if eglDestroySurface is called while
the surface is made current on a thread.

Change-Id: I0df6117a5633c2a19935fe356579abdd76fc471f