Use nested namespace

It's a mechanical change to modernize the code base

src/updater/csv_source.cpp

@@ -25,11 +25,7 @@ namespace
 namespace qi = boost::spirit::qi;
 }
 
-namespace osrm
-{
-namespace updater
-{
-namespace csv
+namespace osrm::updater::csv
 {
 SegmentLookupTable readSegmentValues(const std::vector<std::string> &paths)
 {
@@ -63,6 +59,4 @@ TurnLookupTable readTurnValues(const std::vector<std::string> &paths)
                                                qi::double_ >> -(',' >> qi::double_));
     return parser(paths);
 }
-} // namespace csv
-} // namespace updater
 } // namespace osrm

src/updater/updater.cpp

@@ -61,9 +61,7 @@ template <typename T1, typename T2> struct hash<std::tuple<T1, T2>>
 };
 } // namespace std
 
-namespace osrm
-{
-namespace updater
+namespace osrm::updater
 {
 namespace
 {
@@ -843,5 +841,4 @@ Updater::LoadAndUpdateEdgeExpandedGraph(std::vector<extractor::EdgeBasedEdge> &e
     util::Log() << "Done reading edges in " << TIMER_MSEC(load_edges) << "ms.";
     return number_of_edge_based_nodes;
 }
-} // namespace updater
 } // namespace osrm