converters/osm2pgrouting: fix build after databases/postgresql-libpqxx update

• Uses c++17 and patch CMakeLists.txt (required by databases/postgresql-libpqxx)
• Replace disconnect to close (libpqxx API change) in src/osm_elements/osm2pgrouting.cpp
• While I'm here remove post-install part and update CMakeLists.

Reported by: pkg-fallout