Next time show the object selected, so we can see what objects you have. Now I don't know if the white is object or emty space.
In any way, with the direct selection tool (white pointer) select the right edge of the small orange line and drag it to the left to overlap the left edge. You can hold Shift after start the dragging to constrain horizontally or use the left arrow on your keyboard.
If this doesn't hide the orange line but just move it to the left, in the Pathfinder click the Unite button, deselect all (Shift + Ctrl + A), click with the white pointer on the line and press Delete key on your keyboard.