Changes

testsuite: remove a slow exhaustiveness check (#9555)

The test takes 14s to run every time we run the checksuite, and it
does not seem to serve an easily identifiable purpose. In theory
similar tests could help detect a performance regression in
exhaustiveness checking, but this test seems to only degrade in
constant factor (#9152 proposed to use ocamlc.opt instead of ocamlc to
run it, but it was declined as "hiding" potential problems, which
suggests constant-factor differences). We do not monitor the testsuite
for 10s timing difference, so it is unlikely that we would notice
a constant-factor difference during automated testing.
 (commit: f81e2b6)