ath10k: Remove ath10k_qmi_register_service_notifier() declaration

The ath10k/qmi.h header file contains a declaration for the function
ath10k_qmi_register_service_notifier().  This function doesn't exist.
Remove the declaration.

This patch is a no-op and was just found by code inspection.

Fixes: ba94c753

 ("ath10k: add QMI message handshake for wcn3990 client")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200528122105.1.I31937dce728b441fd72cbe23447bc4710fd56ddb@changeid