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/docs/3.0-migration-guide.md b/docs/3.0-migration-guide.md
index a4a59b8..a30e786 100644
--- a/docs/3.0-migration-guide.md
+++ b/docs/3.0-migration-guide.md
@@ -137,17 +137,13 @@
 to date. If one of your peers is in that case, please try contacting them and
 encouraging them to upgrade their software.
 
-Remove support for compatibility with old Mbed TLS's truncated HMAC
--------------------------------------------------------------------
+Remove support for truncated HMAC
+---------------------------------
 
-This doesn't affect people using the default configuration as it was already
-disabled by default.
-
-This only affects TLS users who enabled `MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT` and
-used the Truncated HMAC extension to communicate with peers using old version
-of Mbed TLS. Please consider using a CCM-8 ciphersuite instead of the
-Truncated HMAC extension, or convincing your peer to upgrade their version of
-Mbed TLS.
+This only affects TLS users who enabled `MBEDTLS_SSL_TRUNCATED_HMAC`
+`MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT` and used the truncated HMAC extension.
+Please consider using a CCM-8 ciphersuite instead of the Truncated HMAC
+extension, or convincing your peer to upgrade their version of Mbed TLS.
 
 Remove support for TLS record-level compression
 -----------------------------------------------