How can I get rid of Contribute 8.x-5.0-beta3 module?
Always you have to first uninstall the module, then remove the codebase from filesystem. 

Composer have nothing to do with installing or uninstalling of modules in drupal. Composer is responsible for downloading the needed files, or removing if not longer in use. 

If you first remove the files from the filesystem, you cannot uninstall it properly, because drupal not knows what to do. 
Therefore you see such errors about missing things. 

What can you do now to get rid of this error if such happen:


Go one step back &amp; put missing files back to filesystem.


If you use git, checkout your last composer.lock before this error, than type composer install to get the old module files back.
Or use your backup or your ftp-program to bring the module files back.

Now you can uninstall the module as you like, perhaps using the gui or with drush (typing drush pmu modulename). This step is important, because it removes all things installed by this module. If you skip this, you will get such errors.
Now delete unwanted module files again: 


checkout your newest state of composer.lock (without that module) 
and type composer install and composer will remove the unwanted files

Don't forget to clear the cache. (drush cr)