Remove USE_PSA from remaining documentation

MBED_TLS_USE_PSA_CRYPTO is now always enabled we need to remove
documentation discussing cases when it is disabled.

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/docs/architecture/psa-migration/psa-limitations.md b/docs/architecture/psa-migration/psa-limitations.md
index 29d7c53..75814f7 100644
--- a/docs/architecture/psa-migration/psa-limitations.md
+++ b/docs/architecture/psa-migration/psa-limitations.md
@@ -21,11 +21,11 @@
 - <https://github.com/Mbed-TLS/mbedtls/issues/7293>;
 - <https://github.com/Mbed-TLS/mbedtls/issues/7294>.
 
-Currently, when `MBEDTLS_USE_PSA_CRYPTO` and `MBEDTLS_ECP_RESTARTABLE` are
-both enabled, some operations that should be restartable are not (ECDH in TLS
-1.2 clients using ECDHE-ECDSA), as they are using PSA instead, and some
-operations that should use PSA do not (signature generation & verification) as
-they use the legacy API instead, in order to get restartable behaviour.
+Currently, when `MBEDTLS_ECP_RESTARTABLE` is enabled, some operations that
+should be restartable are not (ECDH in TLS 1.2 clients using ECDHE-ECDSA), as
+they are using PSA instead, and some operations that should use PSA do not
+(signature generation & verification) as they use the legacy API instead, in
+order to get restartable behaviour.
 
 Things that are in the API but not implemented yet
 --------------------------------------------------