docs: migration-guide-3.5: deduplicate the ram-disk notes

This point ended up being mentioned twice for some reasons.

Signed-off-by: Fabio Baltieri <[email protected]>

doc/releases/migration-guide-3.5.rst

@@ -227,19 +227,6 @@ Device Drivers and Device Tree
   suffix ``dig`` added. For example, ``iomuxc_snvs_wakeup_gpio13_io00`` has
   been renamed to ``iomuxc_snvs_wakeup_dig_gpio13_io00``
 
-* Ramdisk drivers are now instantiated using devicetree. Kconfig options
-  ``CONFIG_DISK_RAM_VOLUME_NAME`` and ``CONFIG_DISK_RAM_VOLUME_SIZE`` have
-  been removed. Instead, instantiate a ramdisk within devicetree like so:
-
-  .. code-block:: devicetree
-
-    ramdisk0 {
-        compatible = "zephyr,ram-disk";
-        disk-name = "RAM";
-        sector-size = <512>;
-        sector-count = <128>;
-    };
-
 Power Management
 ================