Deprecate 'body' as a keyword

[Geod24]

Take 2! Below is the commit message:

This was first deprecated in #10693 (December 2019),
but was then reverted in #10763 to extend the transition period.
Since the replacement will have been available for 22 releases
(almost 4 years), it should be safe to deprecate now.

[dlang-bot]

Thanks for your pull request, @Geod24!

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Testing this PR locally

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dub run digger -- build "master + dmd#12244"

[thewilsonator]

src/undead/bitarray.d(63,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
--
  | src/undead/bitarray.d(74,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(186,9): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(231,9): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(422,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(515,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(555,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(595,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(637,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(677,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(713,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(748,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/bitarray.d(785,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/date.d(568,1): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/regexp.d(2755,5): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/stream.d(1831,3): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/stream.d(2914,3): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.
  | src/undead/stream.d(2932,3): Deprecation: Usage of the `body` keyword is deprecated. Use `do` instead.

[Geod24]

dlang/undeaD#43