Remove USE_PSA references from SSL documentation

MBEDTLS_USE_PSA_CRYPTO is now always enabled we need to update the
documentation accordingly.

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/include/mbedtls/ssl_ciphersuites.h b/include/mbedtls/ssl_ciphersuites.h
index 3e235f3..18e3c4a 100644
--- a/include/mbedtls/ssl_ciphersuites.h
+++ b/include/mbedtls/ssl_ciphersuites.h
@@ -389,7 +389,7 @@
 #endif
 
 /* The handshake params structure has a set of fields called xxdh_psa which are used:
- * - by TLS 1.2 with `USE_PSA` to do ECDH or ECDHE;
+ * - by TLS 1.2 to do ECDH or ECDHE;
  * - by TLS 1.3 to do ECDHE or FFDHE.
  * The following macros can be used to guard their declaration and use.
  */