tests: do not mark ps_sched_batch.exp as untested

tests: do not mark ps_sched_batch.exp as untested

Right now the test case is both testing it (expect_pass "$test") and
marking it as untested (untested "$test"), it should do either one or
the other, so stop marking it as untested.

Before this change, these lines appear in testsuite/ps.log or the output
of `make check RUNTESTFLAGS="--all"`:

  PASS: ps SCHED_BATCH scheduler
  UNTESTED: ps SCHED_BATCH scheduler

Note that the second line is confusing, it's implying that the test is
untested, right after having tested it and indicated it passes.

After this change, only the first line will appear.

Tested that both `make check` and `make distcheck` continue working with
this commit.

Signed-off-by: Filipe Brandenburger <filbranden@google.com>
Signed-off-by: Craig Small <csmall@enc.com.au>