Remove debug line from selftest

Happened to cause a warning about %x vs uint32_t with arm-none-eabi-gcc 4.9
in addition to being useless
diff --git a/library/x509.c b/library/x509.c
index e97f82d..a3e288b 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -1038,8 +1038,6 @@
         if( verbose != 0 )
             mbedtls_printf( "failed\n" );
 
-        mbedtls_printf( "ret = %d, &flags = %04x\n", ret, flags );
-
         return( ret );
     }