PM: sleep: wakeirq: drop unused enable helpers

Drop the wake-irq enable and disable helpers which have not been used
since commit bed57030 ("PM / wakeirq: Fix dedicated wakeirq for
drivers not using autosuspend").

Note that these functions are essentially just leftovers from the first
iteration of the wake-irq implementation where device drivers were
supposed to call these functions themselves instead of PM core (as
is also indicated by the bogus kernel doc comments).

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>