Updates to tools for Python 3 compatibility

[madchutney]

Description

Summary of change

Final changes to support Python 3 in the /tools directory owned by B-Tools.

Documentation

Remove any mention of the tools supporting Python 2 only.

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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)

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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

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Reviewers

@mark-edgeworth
@jamesbeyond

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Release Notes

Python 3 is now supported by the tools.

Summary of changes

No functional changes, code should be equivalent.

Impact of changes

Code should be Python 3 compatible

Migration actions required

None

[ciarmcom]

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

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts

[0xc0170]

This would be good to have reviewed within today to have in 5.15, please review

[bulislaw]

@mark-edgeworth @acabarbaye please review

[0xc0170]

I spoke to @mark-edgeworth , the update will come tomorrow (internal review/tests found some issues)

[mark-edgeworth]

Over-the-shoulder review done with Graham on Monday. All now fixed.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 2
Build artifacts