[C++] Remove Boost::System runtime dependency

[merlimat]

Motivation

Linking with Boost::System was only required by Asio if we were not using C++11 flags. Since this was updated a while ago, we don't need to link with System anymore.

[rdhabalia]

/pulsarbot run-failure-checks

[BewareMyPower]

Hi Matteo, I just have a question. Is there any reference to prove that from 1.69 the Boost::System dependency is not required?

I went to https://www.boost.org/doc/libs/1_69_0/doc/html/boost_asio/using.html#boost_asio.using.dependencies and found

Boost.System for the boost::system::error_code and boost::system::system_error classes.

I've tested Boost 1.74 and 1.75 in my local environment, it worked well without Boost::System dependency. But I'm still curious about whether 1.69 is the first version that doesn't require Boost::System dependency.

[merlimat]

@BewareMyPower Here you go: https://www.boost.org/doc/libs/1_76_0/libs/system/doc/html/system.html#changes_in_boost_1_69

Boost.System is now header-only. A stub library is still built for compatibility, but linking to it is no longer necessary.

[BewareMyPower]

@merlimat Thanks for your guide!