The ornamental design for an extrusion, as shown and described herein.
FIG. 1 is an end perspective view of an extrusion showing my new design, which is shown broken away to indicate unclaimed length;
FIG. 2 is an end elevational view thereof;
FIG. 3 is an enlarged fragmentary end elevational view thereof, showing the top-most portion of FIG. 2, with the remainder omitted for clarity of illustration; and,
FIG. 4 is an enlarged fragmentary end elevational view thereof, showing the bottom-most portion of FIG. 2, with the remainder omitted for clarity of illustration.