The ornamental design for a centerpiece, as shown and described.
FIG. 1 is a front top perspective view of a centerpiece showing our new design;
FIG. 2 is another front top perspective view thereof;
FIG. 3 is a rear top perspective view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a side elevation view thereof, the other three side views being identical; and,
FIG. 7 is an exploded side elevation view thereof, the other three side views being identical.
The evenly spaced broken lines in the drawings are included for the purpose of showing features that form no part of the claimed design. The long and two short broken lines define the bounds of the claimed design and form no part thereof. The long and one short broken lines represent that the flower stem is exploded from the holder.