[Integration tests refactor] __tests__/trust-relationship-send-decline.spec.js

[dadiorchen]

Now we need to refactor all the test under _ _ tests _ _
The problem:
Currently, all the integration tests direct under _ _ tests _ _ are copied from the previous end-to-end tests. And in general, there is a lot of replicated code, and unreadable and hard to maintain. We need to refactor them to an easy way to write and maintain.
There is the example: #192 you can refer to this example to refactor the test, and put the new test file into _ tests _/integration dir, and put mock data into mock-data dir.

This issue/task is to refactor the test: https://github.com/Greenstand/treetracker-wallet-api/blob/master/__tests__/trust-relationship-send-decline.spec.js