Documentation: driver-api: thermal: Remove thermal_notify_framework from documentation

Since thermal_notify_framework is no longer supported/implemented
remove the entry from sysfs-api.rst.

Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210122023406.3500424-4-thara.gopinath@linaro.org