Bug#962288: ros-actionlib build depends on libboost-signals-dev that is removed in boost1.71

[Adrian Bunk]

Source: ros-actionlib
Version: 1.12.0-4
Severity: serious
Tags: ftbfs
Control: block 961995 by -1

https://buildd.debian.org/status/package.php?p=ros-actionlib

libboost-signals-dev is removed in boost1.71.