Remove existing image before creating manifest

[der-eismann]

For some reason there's an increased number of

# Creating manifest 074509403805.dkr.ecr.eu-west-1.amazonaws.com/php-builder:alma9-php8.2
$ /bin/buildah manifest create 074509403805.dkr.ecr.eu-west-1.amazonaws.com/php-builder:alma9-php8.2
Error: creating image to hold manifest list:
 image name "074509403805.dkr.ecr.eu-west-1.amazonaws.com/php-builder:alma9-php8.2" is already associated
 with image "3206bef73d37ebd561ff9eeb72eb4da529b9e06df6411718726d79bdd7ae6400": that name is already in use

So just like we're cleaning up the manifest already, we're now removing images with the same name before creating the manifest.