tests/functional: Remove sleep workarounds from sh4 test

tests/functional: Remove sleep workarounds from sh4 test

These were introduced in the avocado tests to workaround read issues
when interacting with console. They are no longer necessary and we can
use the expected login string instead.

Test always passes now. Remove skipUnless test on QEMU_TEST_FLAKY_TESTS.

Signed-off-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20241122141827.2039984-1-clg@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>