The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a perspective view of a footwear upper in accordance with a third embodiment of our design;
FIG. 2 is a right side view of the footwear upper in accordance with the third embodiment; and,
FIG. 3 is a top elevational view of the footwear upper in accordance with the third embodiment.
Broken lines are environmental only and form no part of the claimed design. Broken lines adjacent shaded areas of the design represent the bounds of the claimed design and are not themselves a part of the claimed design.