With DV always enforced, the "hand written validation" subtest (which
set DeclarativeValidation=off and emulated 1.35) now exercises the
same code path as "Beta disabled". Remove it along with the
MinEmulationVersion option, the WithMinEmulationVersion helper,
deDuplicateErrors, and the now-tautological imperative-vs-declarative
equivalence checks.
Move the existing declarative_validation_test.go files out of
pkg/registry/ into a top-level tree at
test/declarative_validation/<group>/<kind>/. The new location pairs
each hand-written test with the per-Kind TestMain and version-init
files emitted by validation-gen, so the coverage gate runs alongside
the equivalence checks and apiVersions no longer needs to be
hand-maintained.
