The subfunctions are only defined for sse2

See highbd_subpel_variance_impl_sse2.asm

Change-Id: Id13b97f4f6d189ed71cdc6d52b3c4ea63dc1da05
diff --git a/vpx_dsp/x86/highbd_variance_sse2.c b/vpx_dsp/x86/highbd_variance_sse2.c
index 6fabc4a..14d029c 100644
--- a/vpx_dsp/x86/highbd_variance_sse2.c
+++ b/vpx_dsp/x86/highbd_variance_sse2.c
@@ -260,8 +260,7 @@
   DECL(16, opt)
 
 DECLS(sse2);
-// TODO(johannkoenig): enable the ssse3 or delete
-// DECLS(ssse3, ssse3);
+
 #undef DECLS
 #undef DECL