Update the clean target in the testsuite
Update the clean target in the testsuite

This is a follow-up to commit a0fa9aa6e85ca4db9fc19389f89be9ff0d3bd00f

It removes the part of the clean target that invoked `make clean`
recursively. This is no longer needed and produced an error because
the interactive directory on which find was invoked had been removed
in commit f72a4b58f1881669de45228b2cb2059dd2ceabd0.

gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml