Simplify matrix_test.py slightly.
Simplify matrix_test.py slightly.

ManiacalLabs/BiblioPixel,rec/BiblioPixel,rec/BiblioPixel,ManiacalLabs/BiblioPixel,ManiacalLabs/BiblioPixel,rec/BiblioPixel,rec/BiblioPixel,ManiacalLabs/BiblioPixel