backend/local: Remove unused DisablePlanFileStateLineageChecks flag

Now that show command has been refactored to remove its dependence
on a local backend and local run, this flag is no longer needed to
fix #30195.

internal/backend/backend.go

@@ -275,13 +275,6 @@ type Operation struct {
 	// the variables set in the plan are used instead, and they must be valid.
 	AllowUnsetVariables bool
 
-	// When loading a plan file for a read-only operation, we may want to
-	// disable the state lineage checks which are only relevant for operations
-	// which can modify state. An example where this is important is showing
-	// a plan which was prepared against a non-default state file, because the
-	// lineage checks are always against the default state.
-	DisablePlanFileStateLineageChecks bool
-
 	// View implements the logic for all UI interactions.
 	View views.Operation
 

internal/backend/local/backend_local.go

@@ -284,7 +284,7 @@ func (b *Local) localRunForPlanFile(op *backend.Operation, pf *planfile.Reader,
 		))
 		return nil, snap, diags
 	}
-	if !op.DisablePlanFileStateLineageChecks && currentStateMeta != nil {
+	if currentStateMeta != nil {
 		// If the caller sets this, we require that the stored prior state
 		// has the same metadata, which is an extra safety check that nothing
 		// has changed since the plan was created. (All of the "real-world"