code: @PostMapping("/removeEntityMapping")
    public String removeEntityMapping(
        @RequestParam String mappingProjectId, String target, String source) {
      MappingProject project = mappingService.getMappingProject(mappingProjectId);
      project.getMappingTarget(target).removeSource(source);
      mappingService.updateMappingProject(project);
      return "redirect:" + getMappingServiceMenuUrl() + "/mappingproject/" + mappingProjectId;
    }
docs: Removes entity mapping
  
  @param mappingProjectId ID of the mapping project to remove entity mapping from
  @param target entity name of the mapping target
  @param source entity name of the mapping source
  @return redirect url of the mapping project's page