[maint]: Remove use of folly/hash/Hash.h

[ianthomas23]

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Reference Issues/PRs

Fixes the 5th item of the folly replacement plan, issue #1412.

What does this implement or fix?

This removes the single include of folly/hash/Hash.h. The only explicit use of this is folly::hash::hash_combine which I have replaced with use of boost::hash_combine.

It would alternatively be possible to vendor the 3 or so folly functions, but I have rejected this idea. One of the functions is hash_128_to_64 and is taken from cityhash which is essentially unmaintained for 11 years. I would rather use the actively maintained boost.

Any other comments?

There are some tests of folly::hash::commutative_hash_combine in test_hash.cpp, but this function is not used anywhere else in the ArcticDB code base so I have removed the test code as not being relevant.