c54e5a41c4 Remove unreferenced boost headers (Murray Nesbitt)
Pull request description:
Building with clang (e.g. on FreeBSD) is very noisy due to `-Wthread-safety-analysis` warnings regarding boost. This change removes a number of unnecessary boost includes, and silences the rest of the warnings when building with clang. This allows more potentially interesting warnings to surface from the noise.
Tested on FreeBSD 11.2
Tree-SHA512: 5e6a0623188b9be59aeae52866799aefb4c3c9ab5e569b07ee8d43fc92e0b5f1f76b96bb54c35c7043148df84641b4a96927fb71f6eb00460c20cd19cf250900
09f1d7fe72