headers: winnt.h: remove constant SUBLANG_TIBETAN_BHUTAN

This constant is not present in winnt.h from recent Windows SDKs.

This constant has value 0x02; LCID locale created with

	MAKELANGID (LANG_TIBETAN, SUBLANG_TIBETAN_BHUTAN)

is not a valid locale on recent Windows versions.

Signed-off-by: LIU Hao <lh_mouse@126.com>