Remove obsolete code path

This was left in by 7434533 for some reason.

src/seed_rng.cpp

@@ -15,27 +15,13 @@
 /* This file selects a seed source -- "nondeterministic" random number
    generator in boost documentation. It should be a wrapper for
    boost::random_device on platforms where this is available, otherwise
-   it should most likely be the system time.
+   it should most likely be the system time. (Currently boost::random_device
+   is available on all supported platforms.)
 */
 
 #include "seed_rng.hpp"
 
-/*****
-  Use preprocessor tests to decide whether to try to include and
-  use boost random device, or fallback to system time.
- *****/
-
-#define SEED_RNG_USE_BOOST_RANDOM_DEVICE
-
-/*****
-  End preprocessor checks
- *****/
-
-#ifdef SEED_RNG_USE_BOOST_RANDOM_DEVICE
 #include <boost/nondet_random.hpp>
-#else
-#include <ctime>
-#endif
 
 #include <sstream>
 #include <iomanip>
@@ -43,12 +29,8 @@
 namespace seed_rng {
 
 	uint32_t next_seed() {
-	#ifdef SEED_RNG_USE_BOOST_RANDOM_DEVICE
 		static boost::random_device rnd_;
 		return rnd_();
-	#else
-		return static_cast<uint32_t> (std::time(0));
-	#endif
 	}
 
 	std::string next_seed_str() {