Remove outdated traffic editor .project files

[luca-della-vedova]

Bug fix

Fixed bug

.project files for traffic_editor maps are not used anymore since the refactoring took place in traffic_editor's #301. When opening them with traffic_editor a warning is printed and the project failes to load, .building files should be used instead.

Fix applied

This PR removes the deprecated files.

[codebot]

Users running the binary packaged versions of RMF (including traffic-editor) require the .project files in order to be able to open these files, so we might want to hold off on deleting them until we either update the binary packaged versions (currently blocked on a buildfarm upgrade to 20.04 iirc, @marcoag knows more) or we change the instructions in the ros2multirobotbook to suggest building from source as detailed in https://github.com/open-rmf/rmf

[luca-della-vedova]

It's also true however that the current rmf_demo_maps would actually fail building with an outdated binary release of rmf since a lot of packages just went through renaming. For example the package in the release to build maps is called building_map_tools while now it has been renamed to rmf_building_map_tools https://github.com/open-rmf/rmf_demos/blob/main/rmf_demos_maps/CMakeLists.txt#L33 so compilation would actually fail because the package is not found.
Because of all the renaming that happened builds should probably be either full binary or full source until a new release is triggered.