w32: Replace libiconv DLL by iconv feature of libgpg-error.
* configure.ac: Do nor require libiconv for W32. * common/utf8conv.c [W32]: Do not incluce iconv.h. Request libgpg-error iconv macros. (jnlib_iconv): Use ICONV_CONST macro. * build-aux/speedo/w32/inst.nsi [!WITH_GUI]: Do not install libiconv. * build-aux/speedo.mk (speedo_spkgs) [!WITH_GUI]: Likewise.
- Signed-off-by: Werner Koch <wk@gnupg.org>