variance.c: remove highbd sub-4x4 functions

This experiment was abandoned prior to bitstream finalization.
This removes the highbd versions missed in:
  3b0d800186 variance.c: remove sub-4x4 functions

Bug: aomedia:3416
Change-Id: Ibfa7216532e22ebf6d06737c210c3643d1c17339

aom_dsp/variance.c

diff --git a/aom_dsp/variance.c b/aom_dsp/variance.c
index 5fb837d..fbd62ab 100644
--- a/aom_dsp/variance.c
+++ b/aom_dsp/variance.c
@@ -685,9 +685,6 @@
 HIGHBD_VARIANCES(8, 4)
 HIGHBD_VARIANCES(4, 8)
 HIGHBD_VARIANCES(4, 4)
-HIGHBD_VARIANCES(4, 2)
-HIGHBD_VARIANCES(2, 4)
-HIGHBD_VARIANCES(2, 2)
 
 // Realtime mode doesn't use 4x rectangular blocks.
 #if !CONFIG_REALTIME_ONLY