Changelog entry for the removal of config-psa-crypto.h in 2.x

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/remove-config-psa-crypto.txt b/ChangeLog.d/remove-config-psa-crypto.txt
new file mode 100644
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+++ b/ChangeLog.d/remove-config-psa-crypto.txt
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+Changes
+   * Remove configs/config-psa-crypto.h, which was identical to the default
+     configuration except for having some extra cryptographic mechanisms
+     enabled and for unintended differences. This configuration was primarily
+     intended to demonstrate the PSA API, and lost most of its usefulness when
+     MBEDTLS_PSA_CRYPTO_C became enabled by default.