Restrict @requiresLength request tests to clients

[jjant]

Issue #1086

Description of changes:
As discussed in the linked issue, these tests only apply to clients.

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[mtdowling]

IIRC, we want the server to validate that there's a content-length I thought, which means these wouldn't be client only.

[jjant]

@mtdowling We do want to validate that, but that should be a httpMalformedRequestTests suite.
The request in these tests don't actually carry the Content-Length header, so we can't really test anything on the server.

[JordonPhillips]

From the server perspective this tests that whatever you're doing under the hood with content length doesn't fail on a valid length. It can also test that you've exposed it somewhere. In the typescript ssdk, for example, this could be exposed in the context object they pass along. Or it could be a property of whatever you wrap the http request body with.