Relax ifdef's in pk.h by analogy with md.h
diff --git a/include/polarssl/pk.h b/include/polarssl/pk.h
index 29aec30..7a54c71 100644
--- a/include/polarssl/pk.h
+++ b/include/polarssl/pk.h
@@ -45,16 +45,10 @@
  */
 typedef enum {
     POLARSSL_PK_NONE=0,
-#if defined(POLARSSL_RSA_C)
     POLARSSL_PK_RSA,
-#endif
-#if defined(POLARSSL_ECP_C)
     POLARSSL_PK_ECKEY,
     POLARSSL_PK_ECKEY_DH,
-#endif
-#if defined(POLARSSL_ECDSA_C)
     POLARSSL_PK_ECDSA,
-#endif
 } pk_type_t;
 
 /**