coresight: trace id: Remove legacy get trace ID function.

Removes legacy coresight_get_trace_id() function now its use has been
removed from the ETM code.

Signed-off-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230116124928.5440-9-mike.leach@linaro.org