remove classic theme from configure

If you'd use it, you'd get icons from fallback themes.
That I consider misleading.

Change-Id: I I Id1d71ef3f2e90f783d03ef8287f53f05ce4aa9a9

configure.in

@@ -975,7 +975,7 @@ AC_ARG_WITH(vba-package-format,
 AC_ARG_WITH(theme,
     AS_HELP_STRING([--with-theme="theme1 theme2..."],
         [Choose which themes to include. By default those themes with an '*' are included.
-         Possible choices: classic, *crystal, *default (galaxy), *hicontrast, human, industrial, *oxygen, *tango.]),
+         Possible choices: *crystal, *default (galaxy), *hicontrast, human, industrial, *oxygen, *tango.]),
 ,)
 
 AC_ARG_WITH(helppack-integration,
@@ -9613,7 +9613,7 @@ fi
 WITH_THEMES=""
 for theme in $with_theme; do
     case $theme in
-        classic|crystal|default|galaxy|hicontrast|human|industrial|oxygen|tango) : ;;
+        crystal|default|galaxy|hicontrast|human|industrial|oxygen|tango) : ;;
         *) AC_MSG_ERROR([Unknown value for --with-theme: $theme]) ;;
     esac
     WITH_THEMES="$WITH_THEMES $theme"