tests: delete the manual matrix-test

This test program was useful a decade ago when weston_matrix_invert()
was being developed. It was a manual test program that ran for a certain
number of seconds and required human interpretation of numbers to see if
results were acceptable or not. Hence it was foundamentally unsuitable
for CI.

The way it generated random matrices for inversion testing was also very
naive, and it used the determinant value to determine invertability
which is completely bogus. This made it also a bad test for correctness.

Much better speed and correctness testing is implemented in

    https://gitlab.freedesktop.org/pq/fourbyfour



with documented testing procedures. It has a copy of the weston_matrix
implementation.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>