Revert to finding and linking boost headers

Summary: This will unbreak the macos build which requires to look up for the brew installation, and it is more correct for any build anyway as we can enforce the versioning.

Test Plan:
Run the build on macOs
Run the gitian builds
Run the guix build
Run the build on linux

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14009