The ornamental design for heel for footwear, as shown and described.
FIG. 1 is a rear perspective view of a shoe showing my heel design;
FIG. 2 is a left side view of the heel shown in FIG. 1;
FIG. 3 is a right side view of the heel shown in FIG. 1;
FIG. 4 is a rear view of the heel shown in FIG. 1; and,
FIG. 5 is a bottom view of the heel shown in FIG. 1.
The broken line showing of the shoe upper, buckle, heel cap, foot bed, and sole is for illustrative purposes only and forms no part of the claimed design.