x86/mce: 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 x86/mce.  Only compile tested.

v2: Local var work removed from mce_schedule_work() as suggested by
    Borislav.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac@vger.kernel.org