Why uninstall avast? Just do GUI>Settings>Troubleshooting>tick “do not use Chrome as avast default browser”.
From your deaktop…Control Panel>Default Programs>select your choice>click “okay”.
You can uninstall Chrome…Control Panel>Uninstall a Program>click “Chrome”>click “uninstall”.
There is no need to do a clean install of avast.
That is like going around your elbow to get to your thumb. 