Don't set group tags

They are unused in Fedora.

mingw-libpng.spec

@@ -11,8 +11,6 @@ URL:            http://www.libpng.org/pub/png/
 # so look there if you fail to retrieve the version you want
 Source0:        ftp://ftp.simplesystems.org/pub/png/src/libpng16/libpng-%{version}.tar.xz
 
-Group:          Development/Libraries
-
 BuildArch:      noarch
 
 BuildRequires:  mingw32-filesystem >= 95
@@ -139,6 +137,7 @@ rm -rf $RPM_BUILD_ROOT%{mingw64_mandir}
 %changelog
 * Tue Oct 25 2016 Kalev Lember <klember@redhat.com> - 1.6.26-1
 - Update to 1.6.26
+- Don't set group tags
 
 * Sun Oct 16 2016 Kalev Lember <klember@redhat.com> - 1.6.25-1
 - Update to 1.6.25