doc: release: Finalize v3.7.0 release notes and migration guide

Remove working draft status from the v3.7.0 release notes and migration
guide.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

doc/releases/migration-guide-3.7.rst

@@ -2,8 +2,8 @@
 
 .. _migration_3.7:
 
-Migration guide to Zephyr v3.7.0 (Working Draft)
-################################################
+Migration guide to Zephyr v3.7.0
+################################
 
 This document describes the changes required when migrating your application from Zephyr v3.6.0 to
 Zephyr v3.7.0.

doc/releases/release-notes-3.7.rst

@@ -2,8 +2,8 @@
 
 .. _zephyr_3.7:
 
-Zephyr 3.7.0 (Working Draft)
-############################
+Zephyr 3.7.0
+############
 
 We are pleased to announce the release of Zephyr version 3.7.0.