docs: remove stale new.target bytecode pre-gate

[rogeralsing]

Summary

• remove the obsolete pre-gate:newTarget contract ledger row
• document that non-undefined new.target is now owned by constructor/class activation and opcode/compiler support
• update the contract drift guard expected pre-gate set

Verification

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedName~ExpressionProgramCoverageMapTests.UnifiedBytecodeExpansionContract_ListsRequiredHeadingsAndCurrentEnums|FullyQualifiedName~UnifiedBytecodeProductionConstructCallTests.OrdinaryConstructorBody_UsesProductionFastPathWithNewTarget|FullyQualifiedName~UnifiedBytecodeProductionConstructCallTests.Construct_PropagatesNewTargetToConstructor"
• rtk git diff --check

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