tests: posix: timer: do not skip tests

I just happened to try to run this testsuite manually today and
noticed that it was being skipped due to a copy-paste error.

This test was migrated from tests/posix/common, where tests
were skipped for non-dynamic threads, since it would mostly
duplicate tests that had already been run.

However, while migrating, the condition to skip tests was
mistakenly left in when it should not have been.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>