The ornamental design for an earcup, as shown and described.
FIG. 1 is a perspective view, showing the new design for an earcup;
FIG. 2 is a front view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is rear view thereof; and,
FIG. 7 is a bottom view thereof.
The broken line showing forms no part of the claimed design, and the shading is provided to illustrate contour only and is not an indication of texture, gloss, etc.