mkvtoolnix: do not depend on boost with c++11 flag

mkvtoolnix should not depend on boost being built with `--c++11` because then it won't use the bottle and boost takes a long time to compile. C++11 is always nice to have but it is not necessary in this case. The boost bottle is just fine.
Also, there is currently a problem with building boost from source (patch SHA1 changed).

This should fix some of the problem reports in: https://github.com/Homebrew/homebrew/issues/28169