tests: logging: Allow LOG_PRINTK from user space

The commit '3b29b9fa (tests: logging: restore userspace testing,
2025-04-18)' set CONFIG_LOG_PRINTK=n which brakes the build on the
platform 'ip_k66f'.

Without CONFIG_LOG_PRINTK=n (dependency from CONFIG_USERSPACE=y) some
tests in 'tests/subsys/logging/log_core_additional/logging.log_user'
would not build.

Remove this dependency so that LOG_PRINTK can also be used from user
space, which is possible since '77925656 (logging: Fix runtime
message creation in user-mode thread, 2025-04-18)' and reset
CONFIG_LOG_PRINTK=y.

Fixes: #89067
Signed-off-by: Christoph Winklhofer <cj.winklhofer@gmail.com>