cli: Remove no-op plan backend setup

This code does not appear to have any effect. The operation request has
its PlanOutBackend field populated directly in the Meta.Operation
method, by calling m.backendForState.ForPlan().

I tested a trivial null-resource config with a Consul backend, and the
saved plans with and without this code present were identical.

command/plan.go

@@ -8,7 +8,6 @@ import (
 	"github.com/hashicorp/terraform/command/arguments"
 	"github.com/hashicorp/terraform/command/views"
 	"github.com/hashicorp/terraform/configs"
-	"github.com/hashicorp/terraform/plans"
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/hashicorp/terraform/tfdiags"
 )
@@ -108,66 +107,6 @@ func (c *PlanCommand) Run(args []string) int {
 		}
 	}
 
-	// c.Backend above has a non-obvious side-effect of also populating
-	// c.backendState, which is the state-shaped formulation of the effective
-	// backend configuration after evaluation of the backend configuration.
-	// We will in turn adapt that to a plans.Backend to include in a plan file
-	// if opReq.PlanOutPath was set to a non-empty value above.
-	//
-	// FIXME: It's ugly to be doing this inline here, but it's also not really
-	// clear where would be better to do it. In future we should find a better
-	// home for this logic, and ideally also stop depending on the side-effect
-	// of c.Backend setting c.backendState.
-	{
-		// This is not actually a state in the usual sense, but rather a
-		// representation of part of the current working directory's
-		// "configuration state".
-		backendPseudoState := c.backendState
-		if backendPseudoState == nil {
-			// Should never happen if c.Backend is behaving properly.
-			diags = diags.Append(fmt.Errorf("Backend initialization didn't produce resolved configuration (This is a bug in Terraform)"))
-			c.showDiagnostics(diags)
-			return 1
-		}
-		var backendForPlan plans.Backend
-		backendForPlan.Type = backendPseudoState.Type
-		workspace, err := c.Workspace()
-		if err != nil {
-			c.Ui.Error(fmt.Sprintf("Error selecting workspace: %s", err))
-			return 1
-		}
-		backendForPlan.Workspace = workspace
-
-		// Configuration is a little more awkward to handle here because it's
-		// stored in state as raw JSON but we need it as a plans.DynamicValue
-		// to save it in the state. To do that conversion we need to know the
-		// configuration schema of the backend.
-		configSchema := b.ConfigSchema()
-		config, err := backendPseudoState.Config(configSchema)
-		if err != nil {
-			// This means that the stored settings don't conform to the current
-			// schema, which could either be because we're reading something
-			// created by an older version that is no longer compatible, or
-			// because the user manually tampered with the stored config.
-			diags = diags.Append(tfdiags.Sourceless(
-				tfdiags.Error,
-				"Invalid backend initialization",
-				fmt.Sprintf("The backend configuration for this working directory is not valid: %s.\n\nIf you have recently upgraded Terraform, you may need to re-run \"terraform init\" to re-initialize this working directory.", err),
-			))
-			c.showDiagnostics(diags)
-			return 1
-		}
-		configForPlan, err := plans.NewDynamicValue(config, configSchema.ImpliedType())
-		if err != nil {
-			// This should never happen, since we've just decoded this value
-			// using the same schema.
-			diags = diags.Append(fmt.Errorf("Failed to encode backend configuration to store in plan: %s", err))
-			c.showDiagnostics(diags)
-			return 1
-		}
-		backendForPlan.Config = configForPlan
-	}
-
 	// Perform the operation
 	op, err := c.RunOperation(b, opReq)
 	if err != nil {