How to suppress composer autoload when installed as an unused dependecy?
I doubt composer manager is an unused dependency. It would make very little sense to list that module as a dependency and not using it. Are you sure there are no packages listed on yoursite.com/admin/config/system/composer-manager?

It is very likely that the module that defines the dependency requires some composer packages to function properly. Even if you managed to suppress the composer manager module, the main module would not have access to the package that composer was supposed to fetch, and likely will not work as expected. In that case you should consider two things:


Move to a host that gives you more privileges
Download the site to your own computer, install and run composer in the file directory configured on /admin/config/system/composer-manager/settings and re-upload the entire site, including the vendor directory.


If there are really really really no packages, you could try to change composer manager's status in the database system table to 0. That disabled the module without checking for dependencies. It could however break a lot of other things, so have your backups and proceed with caution.