Handle empty bodies the way the channel expects.

[DDEfromOR]

This PR reverts changes to how we handle requests containing activities without bodies to match the behavior expected by the channel SDK. This also creates consistency between requests and responses for handling empty-body activities.

[coveralls]

Pull Request Test Coverage Report for Build 71259

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 77.061%

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Totals
Change from base Build 71130:	0.0%
Covered Lines:	4955
Relevant Lines:	6430

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💛 - Coveralls

[fuselabs]

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