Disable 'body' keyword deprecation

[Geod24]

The replacement for 'body' has been in the language since v2.075.0,
which was released July 2017.
This hasn't been long enough for some corporate users to adapt,
and the main benefit of DIP1003 was to allow to use 'body'
as a keyword, which is already possible nowadays.

Hence, this PR disables the deprecation, with the hope it can be
re-instated either in a few years, or when a more compatible release
management is in place.

CC @don-clugston-sociomantic
This hasn't been released yet.

[dlang-bot]

Thanks for your pull request, @Geod24!

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Testing this PR locally

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dub fetch digger
dub run digger -- build "master + dmd#10763"

[schveiguy]

What is the rationale behind reverting? The explanation in the commit says to see this PR, which has no explanation.

Edit: nevermind. I didn't read the quote, thinking it was from the other PR.

[Geod24]

Another part of the discussion is here: #10757 (comment)

Note that the operator overload deprecation was originally deprecated, then reverted, then re-instantiated (with an slight fix).

The scope qualifier deprecation was also reverted. This one hasn't been dealt with yet, also because while looking at it, I realized scope was just the tip of the iceberg: we have immutable, const, and shared classes and structs. But those don't expose consistent semantics (an example).