[trac3706] Remove unused variables

Remove some unread variables as flagged by cppcheck

src/lib/dhcpsrv/memfile_lease_mgr.cc

@@ -806,8 +806,7 @@ Memfile_LeaseMgr::lfcSetup() {
 template<typename LeaseFileType>
 void Memfile_LeaseMgr::lfcExecute(boost::shared_ptr<LeaseFileType>& lease_file) {
     bool do_lfc = true;
-    // This string will hold a reason for the failure to rote the lease files.
-    std::string error_string = "(no details)";
+
     // Check if the copy of the lease file exists already. If it does, it
     // is an indication that another LFC instance may be in progress or
     // may be stalled. In that case we don't want to rotate the current

src/lib/dhcpsrv/tests/memfile_lease_mgr_unittest.cc

@@ -155,7 +155,6 @@ public:
              ++i) {
             Memfile_LeaseMgr::LFCFileType type = static_cast<
                 Memfile_LeaseMgr::LFCFileType>(i);
-            std::string suffix = Memfile_LeaseMgr::appendSuffix(base_name, type);
             LeaseFileIO io(Memfile_LeaseMgr::appendSuffix(base_name, type));
             io.removeFile();
         }