Log Message:
NetBSD-current provide iconv(3) functionality in libc not
libiconv. Some packages insist on adding '-liconv' during link
or assumes the existent of it with they found iconv.h.

BUILDLINK_TRANSFORM can handle that.
Put it in in libiconv/buildlink2.mk for systematic coverage and
remove it from package "Makefile".

BTW this fix the build of chat/centericq - and probably others - on
-current.

Okayed by jlam@.