[doc] Add release notes for 'account' API removal

Author: jnewbery

doc/release-notes-14023.md

@@ -0,0 +1,8 @@
+Accout API removed
+------------------
+
+The 'account' API was deprecated in v0.17 and has been fully removed in v0.18.
+The 'label' API was introduced in v0.17 as a replacement for accounts.
+
+See the release notes from v0.17 for a full description of the changes from the
+'account' API to the 'label' API.