remove the last bit of boost (#912)

Last bit of #407 - every other occurrence of "boost" when grepping the
repo is in the changelog

image_view/package.xml

@@ -24,7 +24,6 @@
  <depend>camera_calibration_parsers</depend>
  <depend>cv_bridge</depend>
  <depend>image_transport</depend>
- <depend>libboost-dev</depend>
  <depend>message_filters</depend>
  <depend>rclcpp</depend>
  <depend>rclcpp_components</depend>