drm/uapi: Remove unused DRM_DISPLAY_INFO_LEN

Remove the unused DRM_DISPLAY_INFO_LEN from the uapi headers.
I presume the original plan was to expose the display name
via getconnector, but looks like that never happened. So we have
the define for the length of the string but no string anywhere.

A quick scan didn't seem to reveal userspace referencing this
so hopefully we can just nuke it.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190326173401.7329-4-ville.syrjala@linux.intel.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/uapi/drm/drm_mode.h

@@ -33,7 +33,6 @@
 extern "C" {
 #endif
 
-#define DRM_DISPLAY_INFO_LEN	32
 #define DRM_CONNECTOR_NAME_LEN	32
 #define DRM_DISPLAY_MODE_LEN	32
 #define DRM_PROP_NAME_LEN	32