rand: remove getentropy() fallback for macOS < 10.12

src/random.cpp

@@ -315,14 +315,11 @@ void GetOSRand(unsigned char *ent32)
         RandFailure();
     }
 #elif defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)
-    // We need a fallback for OSX < 10.12
-    if (&getentropy != nullptr) {
+    /* getentropy() is available on macOS 10.12 and later.
+     */
     if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
         RandFailure();
     }
-    } else {
-        GetDevURandom(ent32);
-    }
 #elif defined(HAVE_SYSCTL_ARND)
     /* FreeBSD and similar. It is possible for the call to return less
      * bytes than requested, so need to read in a loop.