The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a perspective view of a footwear upper showing my new design;
FIG. 2 is a side elevational view thereof;
FIG. 3 is an opposite side elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines in FIGS. 1-7 represent portions of the footwear that form no part of the claimed design. The broken line located between the exterior and the interior of the footwear upper defines the bounds of the claimed design and forms no part thereof.