Disable all day event, Recurrence,Workspace Fields in Calendar list

Open the Newform.aspx in edit mode( <site>/Calendarlist/Newform.aspx?toolpaneview=2) and add the content editor webpart to below the form and paste the below script in html editor of the content editor web part.

<script type="text/javascript">
function HideField(title){
var header_h3=document.getElementsByTagName("h3") ;

for(var i = 0; i <header_h3.length; i++)
{
    var el = header_h3[i];
    var foundField ;
   if(el.className=="ms-standardheader")
    {
        for(var j=0; j<el.childNodes.length; j++)
        { 
            if(el.childNodes[j].innerHTML == title || el.childNodes[j].nodeValue == title)
            { 
                var elRow = el.parentNode.parentNode ;
                elRow.style.display = "none"; //and hide the row
                foundField = true ;
                break;
            }
        }        
    }
    if(foundField)
        break ;
}
}

HideField("All Day Event");
HideField("Recurrence") ;
HideField("Workspace") ;
</script>

if you want to hide more fields just you need to add field name in the function like HideField("FieldName");