Header row shows the expand button. How to exclude it?

[gabryk91]

I have a gridview with this columns:

<asp:BoundField DataField="IdCliente" HeaderText="IdCliente"
                                InsertVisible="False" ReadOnly="True" SortExpression="IdCliente"
                                Visible="False" />
                            <asp:BoundField DataField="RagSociale" HeaderText="Ragione sociale"
                                SortExpression="RagSociale" />
                            <asp:BoundField DataField="CodCliente" HeaderText="Codice cliente"
                                SortExpression="CodCliente" />
                            <asp:BoundField DataField="Ndipendenti" HeaderText="N dipendenti"
                                SortExpression="Ndipendenti" />
                            <asp:BoundField DataField="Scadenza" HeaderText="Scadenza"
                                SortExpression="Scadenza" DataFormatString="{0:dd/MM/yyyy}" />
                            <asp:BoundField DataField="Directory" HeaderText="Directory"
                                SortExpression="Directory" Visible="false" />
                            <asp:BoundField DataField="Email" HeaderText="Email"
                                SortExpression="Email" />
                            <%--<asp:BoundField DataField="Geolocalizzazione" HeaderText="Geolocalizzazione"
                                    SortExpression="Geolocalizzazione" />--%>
                            <asp:TemplateField SortExpression="Geolocalizzazione">
                                <HeaderTemplate>
                                    <header style="cursor: pointer;" title="Abilita/Disabilita il controllo basato sulla geolocalizzazione">Geoloc.</header>
                                </HeaderTemplate>
                                <ItemTemplate>
                                    <asp:Label ID="lblGeoloc" runat="server" Text='<%# IIf(Eval("Geolocalizzazione") = "1", "Si", "No") %>'></asp:Label>
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField ShowHeader="False" ItemStyle-HorizontalAlign="Right">
                                <ItemTemplate>
                                    <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False"
                                        CommandName="Select" CssClass="btn btn-outline-info" ><i class="fa fa-hand-pointer" title="Seleziona"></i></asp:LinkButton>
                                    &nbsp;<asp:LinkButton ID="LinkButton10" runat="server" CausesValidation="False"
                                        CommandName="Modifica" CssClass="btn btn-outline-info" ><i class="fa fa-pencil-alt" title="Modifica"></i></asp:LinkButton>
                                    &nbsp;<asp:LinkButton ID="LinkButton9" runat="server" CausesValidation="False"
                                        CommandName="Delete" CssClass="btn btn-outline-danger" OnClientClick="return confirm('Questo utente e tutti i dati associati verranno eliminati, confermi?');"><i class="fa fa-trash" title="Elimina"></i></asp:LinkButton>
                                </ItemTemplate>
                            </asp:TemplateField>

the result is this:

This is my code in the gridview databound event:

grdClienti.HeaderRow.Cells(1).Attributes("data-expanded") = "true"
            grdClienti.HeaderRow.Cells(1).Attributes("data-breakpoints") = ""
            grdClienti.HeaderRow.Cells(2).Attributes("data-breakpoints") = ""
            grdClienti.HeaderRow.Cells(3).Attributes("data-breakpoints") = "xs sm"
            grdClienti.HeaderRow.Cells(4).Attributes("data-breakpoints") = "xs sm"
            grdClienti.HeaderRow.Cells(6).Attributes("data-breakpoints") = "xs sm"
            grdClienti.HeaderRow.Cells(7).Attributes("data-breakpoints") = "xs sm"
            grdClienti.HeaderRow.Cells(8).Attributes("data-breakpoints") = "xs sm"
            grdUtenti.HeaderRow.TableSection = TableRowSection.TableHeader

How can I remove the plus sign in the header row? Thanks