How to reverse GrantAccessToProcessIdentity("Domain/User")?

In our SP2013 on-premise farm, we have two web applications. One for standard team sites and one for MySiteHost. These 2 web application are running under two different IIS app pool with two different identity.

Users followed some sites. The users can post newsfeed directly from their Mysite to those team site's newsfeed. However, they encountered error. After investigation, (refer to this site) I ran follow scripts:

$wa= Get-SPWebApplication $WebApp_MySite
$wa.GrantAccessToProcessIdentity($ID_WebApp)
$wa= Get-SPWebApplication $WebApp
$wa.GrantAccessToProcessIdentity($ID_WebApp_Mysite)

It seems fix the problem. However someone told me I don't need to run last 2 lines. It grants unncessary permission to users.

My question is, how can I reverse what I have done?