Does remove contibution option from user profile page in my project will remove this user entirely? Like from activity or from reports?
if you make a Remove Contribution for the user, then on the Activity tab, and if you look at the Reports, the user’s activity is stored anyway.
That is, in Top Members, you can see that user did something in the project, as well as in Activity.
It can be renamed to Removed User, but some record will still remain.