Remove `TraitBase` and `SpecificationBase`

[feltech]

What

Prerequisite: OpenAssetIO/OpenAssetIO-TraitGen#19

Remove the TraitBase (C++ and Python) and SpecificationBase (Python) classes.

Why

During development of OpenAssetIO/OpenAssetIO-TraitGen#11 it became apparent that TraitBase and SpecificationBase should not be part of the core API, but should instead be incorporated into OpenAssetIO-TraitGen.

Acceptance Criteria

• Remove OpenAssetIO test harness locale class.
• Remove TraitBase/SpecificationBase along with resulting defunct things, e.g. TraitPropertyStatus.
• Issues for updates to dependent projects