pkwrite: removing unused/duplicated variables

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/pkwrite.c b/library/pkwrite.c
index 4bb9ac1..8872953 100644
--- a/library/pkwrite.c
+++ b/library/pkwrite.c
@@ -253,8 +253,6 @@
     if (pk_type == MBEDTLS_PK_OPAQUE) {
         psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
         psa_key_type_t key_type;
-        psa_ecc_family_t curve;
-        size_t bits;
 
         if (PSA_SUCCESS != psa_get_key_attributes(key->priv_id,
                                                   &attributes)) {