egl: drop always-false TestOnly option

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>

src/egl/main/egldisplay.h

@@ -152,7 +152,6 @@ struct _egl_display
 
    /* options that affect how the driver initializes the display */
    struct {
-      EGLBoolean TestOnly;    /**< Driver should not set fields when true */
       EGLBoolean UseFallback; /**< Use fallback driver (sw or less features) */
       void *Platform;         /**< Platform-specific options */
    } Options;