This snippet will remove every other key on a selected property starting from 0 or 1

removeOtherKeys.jsx

//Remove every second keyframe for selected property

var start = 0; //Start with 0 or 1

var activeComp = app.project.activeItem;
if(activeComp && activeComp instanceof CompItem){
    var sel = activeComp.selectedProperties;
    if(sel.length > 0){
        app.beginUndoGroup("Remove every 2nd");
        
        sel = sel[0]; //Getting selected parent property

        for(var s = sel.numProperties; s > 0; s--){
            //getting a sub-property with keyframes on it
            if(sel.property(s).isTimeVarying){
                if(sel.property(s).numKeys > 0){
                    sel = sel.property(s);
                    break;
                }
            }
        }

        if(sel.numKeys > 0){
            for(var k = sel.numKeys; k > 0; k--){
                if(k%2 == start){
                    sel.removeKey(k);
                    k--;
                }
            }
        }

        app.endUndoGroup();
    }
}