4
You need to either clear your web-browser's cache (rather than the XOOPS cache) and/or hit the browser's "refresh" button. The favicon.ico will clear eventually anyway, but how long this takes depends on your browser's settings.
Your theme's theme.html file has a hard-coded reference to favicon.ico in the headers. If you don't want your own favicon.ico file to be used then delete this line from theme.html and update your templates via XOOPS admin.
HTH