The field delete icon in the field editor is missing by an error in the CSS:
admin.css:
.field_delete_icon,
.form_delete_icon {
display: none;
float: right;
font-size: 10px;
text-decoration: none;
height: 16px;
line-height: 16px;
padding: 0 0 0 18px;
background-image: url(../images/delete.png)
background-repeat: no-repeat;;
letter-spacing: 0.3pt
}
After the line with background-image: url(../images/delete.png) should be an semicolon.