freeling: stop vendoring boost

[Bo98]

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

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• This was causing problems rather than fixing them. As it was, this had Boost linkage errors if the Boost formula was installed.
• A significant portion of the formula was effort into building a copy of Boost.
• Some of the fixes in the main Boost formula were not transferred here.
• It had horrible Mach-O modification hacks.
• The original motivation was to avoid options which no longer applies.
• Fixes a blocker of Icu4c 66.1 #52481.

[BrewTestBot]

@SMillerDev has triggered a merge.