thermal: gov_step_wise: Delete obsolete comment

Commit 4102c404 ("thermal/core: Remove DROP_FULL and RAISE_FULL")
removes support for THERMAL_TREND_RAISE_FULL/DROP_FULL but leaves the
comment unchanged.

Delete the obsolte comment about THERMAL_TREND_RAISE_FULL/DROP_FULL.

Fixes: 4102c404 ("thermal/core: Remove DROP_FULL and RAISE_FULL")
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>