variance.c: remove sub-4x4 functions

this experiment was abandoned prior to bitstream finalization

Bug: aomedia:3416
Change-Id: I8c109903fe720e339c82392dff4be9202e58b0a5
diff --git a/aom_dsp/variance.c b/aom_dsp/variance.c
index 443aea4..5fb837d 100644
--- a/aom_dsp/variance.c
+++ b/aom_dsp/variance.c
@@ -263,9 +263,6 @@
 VARIANCES(8, 4)
 VARIANCES(4, 8)
 VARIANCES(4, 4)
-VARIANCES(4, 2)
-VARIANCES(2, 4)
-VARIANCES(2, 2)
 
 // Realtime mode doesn't use rectangular blocks.
 #if !CONFIG_REALTIME_ONLY