Changelog entry for the OID module in Mbed TLS 4.0

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/oid.txt b/ChangeLog.d/oid.txt
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+Removals
+   * The library no longer offers interfaces to look up values by OID
+     or OID by enum values.
+     The header <mbedtls/oid.h> now only defines functions to convert
+     between binary and dotted string OID representations, and macros
+     for OID strings that are relevant to X.509.
+     The compilation option MBEDTLS_OID_C no longer
+     exists. OID tables are included in the build automatically as needed.