ACPI thermal: remove two unused functions

When CONFIG_CPU_FREQ=n ...

drivers/acpi/processor_thermal.c:159:12: warning: ‘acpi_thermal_cpufreq_increase’ defined but not used
drivers/acpi/processor_thermal.c:163:12: warning: ‘acpi_thermal_cpufreq_decrease’ defined but not used

Remove unused declaration of ‘acpi_thermal_cpufreq_increase’ and
‘acpi_thermal_cpufreq_decrease’

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>