Move netrcFile to Settings

Also get rid of Settings::processEnvironment(), it appears to be
useless.

src/libmain/shared.cc

@@ -112,7 +112,6 @@ void initNix()
     opensslLocks = std::vector<std::mutex>(CRYPTO_num_locks());
     CRYPTO_set_locking_callback(opensslLockCallback);
 
-    settings.processEnvironment();
     settings.loadConfFile();
 
     startSignalHandlerThread();