Depend on ros_environment for Humble detection (#107)

PR #98 mistakenly removed ros_environment from package.xml. This broke
Humble detection, which had to be worked around in 9b03f97 ("try
detecting Humble in the build farm", 2025-06-10).

This PR adds ros_environment dependency back and removes the Humble
detection workaround.

This also helps with building the package using the Nix package
manager.

Author: wentasah

package.xml

@@ -14,6 +14,7 @@
     <!-- ROS2 dependencies -->
     <buildtool_depend>ament_cmake</buildtool_depend>
 
+    <depend>ros_environment</depend>
     <depend>rclcpp</depend>
     <depend>rcpputils</depend>
     <depend>rosbag2_transport</depend>

src/CMakeLists.txt

@@ -47,7 +47,7 @@ target_link_libraries( TopicPublisherROS2 commonROS)
 message("AMENT_PREFIX_PATH = ${AMENT_PREFIX_PATH}")
 message("ROS_DISTRO (env) = $ENV{ROS_DISTRO}")
 
-if("${AMENT_PREFIX_PATH}" STREQUAL "/opt/ros/humble" OR "$ENV{ROS_DISTRO}" STREQUAL "humble")
+if("$ENV{ROS_DISTRO}" STREQUAL "humble")
         message(STATUS "Detected Humble")
         target_compile_definitions(DataLoadROS2 PUBLIC ROS_HUMBLE)
         target_compile_definitions(TopicPublisherROS2 PUBLIC ROS_HUMBLE)