rest.ReadRESTReq() is commonly misused

[alessio]

E.g.

		err := rest.ReadRESTReq(w, r, cdc, &req)
		if err != nil {
			rest.WriteErrorResponse(w, http.StatusBadRequest, err.Error())
			return
		}

There is no need to handle/write the error response as ReadRESTReq does that on its own.

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[jackzampolin]

Looks to be addressed in one of your PRs @alessio