backmp11: Remove unneeded header inclusions

[chandryan]

Description

The backend backmp11 successfully resolved long compilation times of big state machines by migrating compile-time intensive metaprogramming usages from MPL to Mp11 (see https://github.com/chandryan/fsm-benchmarks).

There is more optimization potential considering the static parts of the compilation time: Preprocessing the included headers takes roughly 2 seconds. From a compile time trace the following candidates look promising to further reduce the compilation time:

• fusion is used a lot in the frontend, requires more discussion
• bind has only 3 occurrences left
• proto can be removed when cutting off eUML compatibility
• make boost::serialization inclusion opt-in
• mpl_graph is also worth a shot