- Update URL to reflect new location of Boost sources

- Update to version 1.71.0
Breaking changes:
* Uuid: MD5 name-based uuid generation was corrected to be identical
on all endian systems. Define BOOST_UUID_COMPAT_PRE_1_71_MD5 to
keep the result in a format compatible with 1.66 through 1.70.
This does not affect the default name-based uuid generation
which is based on SHA1
* Test: Boost.Test shows deprecation warnings if some very old
headers as deprecated. If you encounter such warnings, please
follow the indications: those headers will be removed in a future
release.
New libraries:
* Variant2: A never-valueless, strong guarantee implementation
of std::variant
Updated libraries:
* align, asio, any, beast, circular buffer, container, context,
conversion, core, dynamic bitset, endian, fiber, filesystem,
flyweight, histogram, iostreams, interprocess, intrusive,
legical cast, log, math, metaparse, move, multi array,
multi-index containers, outcome, parameter, ptrcontainer,
polycollection, smartptr, stacktrace, test, utility, uuid,
variant, yap
For detailed changes see
https://www.boost.org/users/history/version_1_71_0.html
- drop upstream patches no longer needed:
boost-1.57.0-python-libpython_dep.patch,
0001-beast-fix-moved-from-executor.patch,
remove_boost_serialization_depends, cmake.patch