This is rendered as part of the sectionheader tag, but unfortunately there is no attribute on this tag to remove the icon, so you have a few choices
(1) Use JavaScript to find the image and hide it - fragile as Salesforce may change the way that the image is generated (2) See if you can override the image style (or a parent container) to add the display:none CSS attribute - also fragile as Salesforce may change their styling (3) Create your own sectionheader-type tag which just displays title/subtitle. This is the way that I would approach it.
(1) Use JavaScript to find the image and hide it - fragile as Salesforce may change the way that the image is generated
(2) See if you can override the image style (or a parent container) to add the display:none CSS attribute - also fragile as Salesforce may change their styling
(3) Create your own sectionheader-type tag which just displays title/subtitle. This is the way that I would approach it.