[Validator] Removed legacy validator classes
minor #11587 [Validator] Removed legacy validator classes (webmozart)

This PR was merged into the 2.5 branch.

Discussion
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[Validator] Removed legacy validator classes

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This PR removes the legacy validator classes again and adds the API checks inside the constraint validators instead.

Commits
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e844ed0 [Validator] Removed legacy validator classes