The ornamental design for the wall sconce, as shown and described.
FIG. 1 is a bottom front isometric view of our new wall sconce design;
FIG. 2 is a top front isometric view thereof;
FIG. 3 is a top rear isometric view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a rear elevation view thereof;
FIG. 6 is a right side elevation view thereof;
FIG. 7 is a left side elevation view thereof;
FIG. 8 is a top plan view thereof; and,
FIG. 9 is a bottom plan view thereof.
The broken dash lines shown in the drawing views represent unclaimed portions of the design, and neither the lines themselves nor anything within the lines form any part of the claimed invention.