iconv: remove redundant file - we now use libiconv-2.dll

No file in mingw/bin is linked to libiconv2.dll any more.

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>
iconv: include iconv.exe in the Git for Windows release.

As discussed in issue #113 it is useful to have a method for converting
between unicode and utf-8 for writing smudge/clean filters. To assist in
this we shall include a functional iconv.exe in the release.
A side effect is we now also ship libintl-8.dll.

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>