Revert "workqueue: Provide one lock class key per work_on_cpu() callsite"

This reverts commit f9d3ba62 which is
commit 265f3ed0 upstream.

It turns the work_on_cpu() function into an #define, which messes with
the systems that were previously depending on that abi symbol.  As this
is a change only for when lockdep is enabled, which is NOT in any
running Android system, it is safe to revert for now.

Bug: 161946584
Change-Id: I5f117cccfb411efb742a4faf1cefcb4826faae15
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>