doc: releases: Revert change to the migration guide

No migration necessary for this feature.

Signed-off-by: Rodrigo Peixoto <[email protected]>

Author: rodrigopex

doc/releases/migration-guide-4.2.rst

@@ -305,13 +305,6 @@ SPI
 Other subsystems
 ****************
 
-ZBus
-====
-
-* The function :c:func:`zbus_chan_add_obs` now requires a :c:struct:`zbus_observer_node` as an argument,
-  which was previously allocated through :c:func:`k_malloc` internally. The structure must remain valid
-  in memory until :c:func:`zbus_chan_rem_obs` is called.
-
 Modules
 *******