remove WIDE_REFERENCE definition

The last usage was removed in 2011:
https://chromium.googlesource.com/webm/libvpx/+/cbf923b12cec2fe7ceea0b94091d64953e56b1fe%5E%21/#F33

Change-Id: I6e837e6f1e55eeea6bbeb3159ce6ddf861bcbd72
1 file changed