Use pk_load_file() in X509

Saves a bit of ROM. X509 depends on PK anyway.
diff --git a/include/polarssl/pk.h b/include/polarssl/pk.h
index 0ff5f1e..b29eb74 100644
--- a/include/polarssl/pk.h
+++ b/include/polarssl/pk.h
@@ -638,6 +638,14 @@
                      const pk_context *key );
 #endif /* POLARSSL_PK_WRITE_C */
 
+/*
+ * Internal module functions. You probably do not want to use these unless you
+ * know you do.
+ */
+#if defined(POLARSSL_FS_IO)
+int pk_load_file( const char *path, unsigned char **buf, size_t *n );
+#endif
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/include/polarssl/x509.h b/include/polarssl/x509.h
index 3fe6820..5f71881 100644
--- a/include/polarssl/x509.h
+++ b/include/polarssl/x509.h
@@ -307,7 +307,6 @@
                      x509_buf *serial );
 int x509_get_ext( unsigned char **p, const unsigned char *end,
                   x509_buf *ext, int tag );
-int x509_load_file( const char *path, unsigned char **buf, size_t *n );
 int x509_sig_alg_gets( char *buf, size_t size, const x509_buf *sig_oid,
                        pk_type_t pk_alg, md_type_t md_alg,
                        const void *sig_opts );