Modifies ChangeLog and Migration Guide

Entries in ChangeLog and Migration guide files
have been merged to cover both the removal of
MBEDTLS_SSL_TRUNCATED_HMAC and
MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT.

Signed-off-by: Thomas Daubney <thomas.daubney@arm.com>
diff --git a/ChangeLog.d/rm-truncated-hmac-ext.txt b/ChangeLog.d/rm-truncated-hmac-ext.txt
index c82415b..3739256 100644
--- a/ChangeLog.d/rm-truncated-hmac-ext.txt
+++ b/ChangeLog.d/rm-truncated-hmac-ext.txt
@@ -1,4 +1,5 @@
 Removals
-   * Remove MBEDTLS_SSL_TRUNCATED_HMAC config option. Users are better served by
+   * Remove MBEDTLS_SSL_TRUNCATED_HMAC and also remove
+     MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT config option. Users are better served by
      using a CCM-8 ciphersuite than a CBC ciphersuite with truncated HMAC.
-     Addresses #4341.
+     See issue #4341 for more details.