Add flag for removing deprecated API

Add the compile time option PSA_PRE_1_0_KEY_DERIVATION. If this is not
turned on, then the function `psa_key_derivation()` is removed.

Most of the tests regarding key derivation haven't been adapted to the
new API yet and some of them have only been adapted partially. When this
new option is turned off, the tests using the old API and test cases
using the old API of partially adapted tests are skipped.

The sole purpose of this option is to make the transition to the new API
smoother. Once the transition is complete it can and should be removed
along with the old API and its implementation.
diff --git a/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index b08f46d..3675ac6 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -224,6 +224,17 @@
 psa_status_t mbedtls_psa_inject_entropy(const unsigned char *seed,
                                         size_t seed_size);
 
+/*
+ * If this option is not turned on, then the function `psa_key_derivation()`
+ * is removed.
+ *
+ * The sole purpose of this option is to make the transition to the new API
+ * smoother. Once the transition is complete it can and should be removed
+ * along with the old API and its implementation.
+ */
+#define PSA_PRE_1_0_KEY_DERIVATION
+
+#if defined(PSA_PRE_1_0_KEY_DERIVATION)
 /** Set up a key derivation operation.
  *
  * FIMXE This function is no longer part of the official API. Its prototype
@@ -280,6 +291,7 @@
                                 const uint8_t *label,
                                 size_t label_length,
                                 size_t capacity);
+#endif /* PSA_PRE_1_0_KEY_DERIVATION */
 
 /* FIXME Deprecated. Remove this as soon as all the tests are updated. */
 #define PSA_ALG_SELECT_RAW                      ((psa_algorithm_t)0x31000001)