Left Navigation for Weppart Page

Open the webpart page in the Sharepoint Designer and remove the following tags
<asp:Content ContentPlaceHolderId="PlaceHolderLeftNavBar" runat="server"></asp:Content>
<&asp:Content ContentPlaceHolderId="PlaceHolderNavSpacer" runat="server"></asp:Content>

And save the file back, on the warning for customization press Yes