TESTS: Fix integration tests

[jamesbeyond]

Description

Summary of change

PR #11943 introduced a bug, this PR fixed it.

• removed the unneeded common header file based on the PR Split integration tests in fs/net #11943
• moving mbed_trace.h to the test header file

This would be better to go in 5.15 rc

Documentation

not required

---

Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---

Reviewers

@0xc0170 @MarceloSalazar

---

Release Notes

Summary of changes

Impact of changes

Migration actions required

[ciarmcom]

@jamesbeyond, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 5 of 5 test jobs passed
Build number : 1
Build artifacts