thinkpad_acpi: don't use [delayed_]work_pending()

There's no need to test whether a (delayed) work item in pending
before queueing, flushing or cancelling it.  Most uses are unnecessary
and quite a few of them are buggy.

Remove unnecessary pending tests from thinkpad_acpi.  Only compile
tested.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: ibm-acpi-devel@lists.sourceforge.net
Cc: platform-driver-x86@vger.kernel.org