input/nfs: move nfs_domain to lib/nfs/Domain.cxx

src/input/plugins/NfsInputPlugin.cxx

@@ -21,9 +21,9 @@
 #include "NfsInputPlugin.hxx"
 #include "../InputStream.hxx"
 #include "../InputPlugin.hxx"
+#include "lib/nfs/Domain.hxx"
 #include "util/StringUtil.hxx"
 #include "util/Error.hxx"
-#include "util/Domain.hxx"
 
 extern "C" {
 #include <nfsc/libnfs.h>
@@ -32,8 +32,6 @@ extern "C" {
 #include <sys/stat.h>
 #include <fcntl.h>
 
-static constexpr Domain nfs_domain("nfs");
-
 class NfsInputStream {
 	InputStream base;