Move initLibUtil() from initNix to initLibStore

libutil is a dependency of libstore, so it should always be
initialized as such.
libutil is also a dependency of libmain. Being explicit about this
dependency might be good, but not worth the slight code complexity
until the library structure gets more advanced.

Part of an effort to make it easier to initialize the right things,
by moving code into the appropriate libraries.

src/libmain/shared.cc

@@ -118,7 +118,6 @@ void initNix()
     std::cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
 #endif
 
-    initLibUtil();
     initLibStore();
 
     startSignalHandlerThread();