Deprecated signals library was dropped in 1.69.0 release:
https://www.boost.org/users/history/version_1_69_0.html
Signals (v1) is now removed. Its removal was announced in 1.68 and its
deprecation was announced in 1.54. Boost 1.68 is the last release that
provides this library. Users are encouraged to use Signals2 instead. The
Boost community thanks Douglas Gregor for his work on Signals which
served its users well and which also inspired Signals2.
Ros code already uses signals2 library but it still has links to the
older library in its CMake files. This commit removes those references
as they are now useless and more importantly source of error at
configure time.
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
a6af8c051e