Remove Armv8.4 Neon DotProd 4x4 variance kernel

The Armv8.0 Neon implementation is faster for 4x4 blocks.

This is a port from SVT-AV1:
https://gitlab.com/AOMediaCodec/SVT-AV1/-/merge_requests/2608

Originally authored by: Jonathan Wright <Jonathan.Wright@arm.com>

Change-Id: I458e70c618b9b067cd6d6ccbdb37289383fa04ed
diff --git a/aom_dsp/aom_dsp_rtcd_defs.pl b/aom_dsp/aom_dsp_rtcd_defs.pl
index 7a5a615..776d272 100755
--- a/aom_dsp/aom_dsp_rtcd_defs.pl
+++ b/aom_dsp/aom_dsp_rtcd_defs.pl
@@ -1404,7 +1404,7 @@
   specialize qw/aom_variance8x8       sse2      neon neon_dotprod/;
   specialize qw/aom_variance8x4       sse2      neon neon_dotprod/;
   specialize qw/aom_variance4x8       sse2      neon neon_dotprod/;
-  specialize qw/aom_variance4x4       sse2      neon neon_dotprod/;
+  specialize qw/aom_variance4x4       sse2      neon/;
 
   specialize qw/aom_sub_pixel_variance128x128   avx2 neon ssse3/;
   specialize qw/aom_sub_pixel_variance128x64    avx2 neon ssse3/;
diff --git a/aom_dsp/arm/variance_neon_dotprod.c b/aom_dsp/arm/variance_neon_dotprod.c
index dd03443..3a3965e 100644
--- a/aom_dsp/arm/variance_neon_dotprod.c
+++ b/aom_dsp/arm/variance_neon_dotprod.c
@@ -178,7 +178,7 @@
     return *sse - (uint32_t)(((int64_t)sum * sum) >> shift);                  \
   }
 
-VARIANCE_WXH_NEON_DOTPROD(4, 4, 4)
+// The Armv8.0 Neon implementation is faster than Neon DotProd for 4x4.
 VARIANCE_WXH_NEON_DOTPROD(4, 8, 5)
 
 VARIANCE_WXH_NEON_DOTPROD(8, 4, 5)
diff --git a/test/variance_test.cc b/test/variance_test.cc
index c95183f..2a1bf4f 100644
--- a/test/variance_test.cc
+++ b/test/variance_test.cc
@@ -3661,7 +3661,6 @@
   VarianceParams(3, 3, &aom_variance8x8_neon_dotprod),
   VarianceParams(3, 2, &aom_variance8x4_neon_dotprod),
   VarianceParams(2, 3, &aom_variance4x8_neon_dotprod),
-  VarianceParams(2, 2, &aom_variance4x4_neon_dotprod),
 #if !CONFIG_REALTIME_ONLY
   VarianceParams(2, 4, &aom_variance4x16_neon_dotprod),
   VarianceParams(4, 2, &aom_variance16x4_neon_dotprod),