[NaCl SDK] Remove invalid assert from nacl_io.

native_client_sdk/src/examples/demo/voronoi/voronoi.cc

Index: native_client_sdk/src/examples/demo/voronoi/voronoi.cc
diff --git a/native_client_sdk/src/examples/demo/voronoi/voronoi.cc b/native_client_sdk/src/examples/demo/voronoi/voronoi.cc
index 99c2cbb69f2aa41112d084540633357092f451ac..48f311871ff8336fd67ba107683d0495086c87df 100644
--- a/native_client_sdk/src/examples/demo/voronoi/voronoi.cc
+++ b/native_client_sdk/src/examples/demo/voronoi/voronoi.cc
@@ -60,10 +60,13 @@ inline void rand_reset(unsigned int seed) {
   g_rand_state = seed;
 }
 
+#ifndef NDEBUG
 // returns true if input is power of two.
+// only used in assertions.
 inline bool is_pow2(int x) {
   return (x & (x - 1)) == 0;
 }
+#endif
 
 inline double getseconds() {
   const double usec_to_sec = 0.000001;