bsim boards: doc: Fix around printk backend

The printk backend for the bsim boards and native_posix was
merged into a single backend reusable for all POSIX arch boards.
Correct the bsim board documentation so it does
not refer to the old backend anymore.

Signed-off-by: Alberto Escolar Piedras <[email protected]>

Author: aescolar

boards/posix/doc/bsim_boards_design.rst

@@ -225,15 +225,14 @@ which relies on the bs_trace API. Instead, for tracing the bs_trace API
 should be used directly.
 The same applies to other Zephyr APIs, including the entropy API, etc.
 
-printk and posix_print backend
-==============================
-
-The bsim board provides a very simple backend for Zephyr's :c:func:`printk()`,
-which simply routes the printk strings to the bs_trace bsim API.
-So printk messages are printed in the console (stdout) together with all
-other device messages.
-The board also provides the posix_print API which is expected by the posix ARCH
-and soc inf code, and which is based on the same bs_trace API.
+posix_print backend
+===================
+
+The bsim board provides a backend for the posix_print API which is expected by the posix ARCH
+and soc inf (POSIX) code.
+It simply routes the printk strings to the bs_trace bsim API.
+Any message printed to the posix_print API, which is also the default printk backend,
+will be printed to the console (stdout) together with all other device messages.
 
 .. _bsim_boards_bs_tests: