[trivial] Reuse translation and cleanup DEFAULT_* values

* DEFAULT_DISABLE_SAFEMODE = false
* Use DEFAULT_* constants for extern bools

src/script/standard.h

@@ -13,6 +13,8 @@
 
 #include <stdint.h>
 
+static const bool DEFAULT_ACCEPT_DATACARRIER = true;
+
 class CKeyID;
 class CScript;