[c++] Remove Boost min version from CHANGELOG
[c++] Remove Boost min version from CHANGELOG

This change has not yet been made, as it breaks the current AppVeyor
build.

Issue https://github.com/Microsoft/bond/issues/845 has been opened to
remind us to bump the minimum version later.

[skip ci]
Microsoft/bond,Microsoft/bond,chwarr/bond,jdubrule/bond,Microsoft/bond,Microsoft/bond,chwarr/bond,jdubrule/bond,jdubrule/bond,chwarr/bond,chwarr/bond,jdubrule/bond,jdubrule/bond,Microsoft/bond,chwarr/bond,chwarr/bond,jdubrule/bond,Microsoft/bond