debug: remove PRINTK from EXCEPTION_STACK_TRACE

The `PRINTK` was required for `EXCEPTION_STACK_TRACE` because
it's initial implementation for x86 in #6653 uses `printk()`.
We are using `LOG_ERR()` now, so this is not required anymore.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>