cpufreq: Remove references to 10ms min sampling rate

A minimum sampling rate value of 10ms was introduced in:
commit cef9615a ("[CPUFREQ] ondemand: Uncouple minimal sampling rate from HZ in NO_HZ case")

The use of this value was removed in:
commit ed4676e2 ("cpufreq: Replace "max_transition_latency" with "dynamic_switching"")

Remove:
- a comment referencing this value
- an unused macro associated to this value

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>