I claim the ornamental design for a hair trimmer housing, as shown and described.
FIG. 1 is a perspective view of a hair trimmer housing.
FIG. 2 is a top view of the design shown in FIG. 1.
FIG. 3 is a bottom view of the design shown in FIG. 1.
FIG. 4 is a right view of the design shown in FIG. 1.
FIG. 5 is a left view of the design shown in FIG. 1.
FIG. 6 is a front view of the design shown in FIG. 1; and,
FIG. 7 is a rear view of the design shown in FIG. 1.
The present application is directed to the shape and contour of the designs illustrated in the drawings. The broken line showing of the environment is for illustrative purposes only and forms no part of the claimed designs.