Brown sugar does contain corn because brown sugar is made up with around 88 percent of sucrose with is derived from corn.
So although the corn cannot really be seen or tasted in the brown sugar the brown sugar does contain some corn for the corn syrup that it contains.
Codex Alimentarius requires brown sugar to contain at least 88 percent of sucrose as well as invert sugar and commercial brown sugar contains from 3.5% molasses to 6.5% molasses based on total volume.
So if you cannot eat corn then you may want to or should avoid brown sugar because it does contain some corn but not directly since it's in the sucrose that is derived from corn.