Remove all user groups from a web site in javascript

How to delete SP.Group in SharePoint 2013 via JSOM

Use SP.GroupCollection.remove, SP.GroupCollection.removeById or SP.GroupCollection.removeByLoginName methods to remove Group from site.

Example

var context = SP.ClientContext.get_current();
var groups = context.get_web().get_siteGroups();
groups.removeById(groupId);

context.executeQueryAsync(
    function() {
          console.log('Group is deleted');
    },
    function(sender, args) {
           console.log(args.get_message());
    }    
);

In your case it is not clear why you need to remove all the groups where user belongs to, but the following script demonstrates how to perform that:

var context = SP.ClientContext.get_current();
var user = context.get_web().getUserById(userId);
context.load(user,'Groups');
context.executeQueryAsync(
   function() {
       var groups = user.get_groups();
       for(var i = 0; i < groups.get_count();i++) {
           var group = groups.getItemAtIndex(i);
           groups.removeByLoginName(group.get_loginName());
       }


       context.executeQueryAsync(
          function() {
             console.log('Completed'); 
          },
          function(sender, args) {
             console.log(args.get_message());
          }    
       );


    },
    function(sender, args) {
        console.log(args.get_message());
    }    
);