Remove deprecated backends in v1.3.0 (#159)

This removes the following backends that were removed in Terraform v1.3.0:

- azure (only this name was deprecated, the azurerm backend still exists)
- artifactory
- etcd
- etcdv3
- manta
- swift

This was removed in hashicorp/terraform#31711

internal/schema/backends/backends.go

@@ -20,6 +20,7 @@ var (
  v0_13_1 = version.Must(version.NewVersion("0.13.1"))
  v0_14_0 = version.Must(version.NewVersion("0.14.0"))
  v0_15_0 = version.Must(version.NewVersion("0.15.0"))
+ v1_3_0 = version.Must(version.NewVersion("1.3.0"))
 )
 
 func BackendTypesAsExprConstraints(tfVersion *version.Version) schema.ExprConstraints {
@@ -127,5 +128,17 @@ func backendBodySchemas(v *version.Version) map[string]*schema.BodySchema {
  delete(backends, "atlas")
  }
 
+ if v.GreaterThanOrEqual(v1_3_0) {
+ // https://github.com/hashicorp/terraform/commit/aa48af6e
+ delete(backends, "azure")
+ delete(backends, "artifactory")
+ delete(backends, "manta")
+ delete(backends, "swift")
+ // https://github.com/hashicorp/terraform/commit/799ab6c9
+ delete(backends, "etcd")
+ // https://github.com/hashicorp/terraform/commit/d61d3e9f
+ delete(backends, "etcdv3")
+ }
+
  return backends
 }