/Views/Shared/_ColumnsTwo.cshtml
look for this line:
@Html.Action("CategoryNavigation", "Catalog", new { currentCategoryId = currentCategoryId, currentProductId = currentProductId })
..and this line should be just below it:
@Html.Action("PopularProductTags", "Catalog")
You just need to comment those two lines out, like this:
@* @Html.Action("CategoryNavigation", "Catalog", new { currentCategoryId = currentCategoryId, currentProductId = currentProductId }) *@
@* @Html.Action("PopularProductTags", "Catalog") *@