Remove vrt2, vkrn, vpal, and valt from default vertical features

See thread by John Dagget on the list.

TODO

@@ -5,8 +5,6 @@ General fixes:
 
 - Return "safe-to-break" bit from shaping.
 
-- Disable 'vert' if 'vrt2' is available (eg. Motoya fonts with arrow chars).
-
 - Implement 'rand' feature.
 
 - mask propagation? (when ligation, "or" the masks).

src/hb-ot-shape.cc

@@ -58,17 +58,8 @@ static hb_tag_t horizontal_features[] = {
   HB_TAG('r','c','l','t'),
 };
 
-/* Note:
- * Technically speaking, vrt2 and vert are mutually exclusive.
- * According to the spec, valt and vpal are also mutually exclusive.
- * But we apply them all for now.
- */
 static hb_tag_t vertical_features[] = {
-  HB_TAG('v','a','l','t'),
   HB_TAG('v','e','r','t'),
-  HB_TAG('v','k','r','n'),
-  HB_TAG('v','p','a','l'),
-  HB_TAG('v','r','t','2'),
 };