libobs-opengl: Close display when destroying X11/EGL platform
Currently, the X11 display may be leaked when the X11/EGL
platform is destroyed. Fix that by calling XCloseDisplay()
to free it.
Fixes: 2fd8a6df557766 ("libobs-opengl: Introduce the X11/EGL winsys")
(cherry picked from commit 8e96d47cd3d94213da52277678d844ef616d08a2)