iwlwifi: acpi: remove unused function iwl_acpi_eval_dsm_func()

Stephen reported a warning:

drivers/net/wireless/intel/iwlwifi/fw/acpi.c:720:12: warning: 'iwl_acpi_eval_dsm_func' defined but not used [-Wunused-function]

The warning is correct and the function is not used anywhere, so let's
just remove it.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 7119f02b ("iwlwifi: mvm: support BIOS enable/disable for 11ax in Russia")
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Acked-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210624052918.4946-1-kvalo@codeaurora.org