Fix malformed package.xml for ROS2 colcon builds

The package.xml had two <package> root elements which is invalid XML.
This caused colcon to fail to parse it, preventing ROS2 builds from
finding the reactor-cpp package.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: lsk567

package.xml

@@ -10,13 +10,3 @@
    <build_type>cmake</build_type>
  </export>
 </package>
-<package format="3">
- <name>reactor-cpp-foo</name>
- <version>0.0.0</version>
- <description>A C++ reactor runtime</description>
- <maintainer email="[email protected]">user</maintainer>
- <license>ISC License</license>
- <export>
-   <build_type>cmake</build_type>
- </export>
-</package>