x86/mce/inject: Remove call to mce_notify_irq()

The call to mce_notify_irq() has been there since the initial version of
the soft inject mce machinery, introduced in

  ea149b36 ("x86, mce: add basic error injection infrastructure").

At that time it was functional since injecting an MCE resulted in the
following call chain:

  raise_mce()
    ->machine_check_poll()
        ->mce_log() - sets notfiy_user_bit
  ->mce_notify_user() (current mce_notify_irq) consumed the bit and called the
  usermode helper.

However, with the introduction of

  011d8261 ("RAS: Add a Corrected Errors Collector")

the code got moved around and the usermode helper began to be called via the
early notifier mce_first_notifier() rendering the call in raise_local()
defunct as the mce_need_notify bit (ex notify_user) is only being set from the
early notifier.

Remove the noop call and make mce_notify_irq() static.

No functional changes.

Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250225143348.268469-1-nik.borisov@suse.com