[minor] Remove comment about Navajo OpenType code.
Apparently the code is already standardized:
https://www.microsoft.com/typography/otspec/languagetags.htm
diff --git a/src/hb-ot-tag.cc b/src/hb-ot-tag.cc
index 160c80e..aac7c6d 100644
--- a/src/hb-ot-tag.cc
+++ b/src/hb-ot-tag.cc
@@ -542,7 +542,7 @@
{"nr", HB_TAG('N','D','B',' ')}, /* [South] Ndebele */
{"nsk", HB_TAG('N','A','S',' ')}, /* Naskapi */
{"nso", HB_TAG('S','O','T',' ')}, /* [Northern] Sotho */
- {"nv", HB_TAG('N','A','V',' ')}, /* Navajo (not standardized yet) */
+ {"nv", HB_TAG('N','A','V',' ')}, /* Navajo */
{"ny", HB_TAG('C','H','I',' ')}, /* Chewa/Chichwa/Nyanja */
{"nym", HB_TAG('N','Y','M',' ')}, /* Nyamwezi */
{"nyn", HB_TAG('N','K','L',' ')}, /* Nyankole */
