provider/azurerm: fix key_vault docs mentioning ServiceBus
provider/azurerm: fix key_vault docs mentioning ServiceBus

thiagocaiubi/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm,sebastus/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,sebastus/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,sebastus/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm