title: Upgrading terraform provider results in "invalid resource instance data in state" errors
body: <p>I upgraded my Terraform AzureRM provider from 1.44 to 2.23. Terraform version is 0.13.0. Interestingly now that I try to run <code>terraform plan</code> I get multiple &quot;Invalid resource instance data in state&quot; errors.</p>
  <p>They look like this:</p>
  <pre><code>Error: Invalid resource instance data in state
  
    on .terraform\modules\redacted\terraform\modules\keyvault\main.tf line 1:
     1: resource &quot;azurerm_key_vault&quot; &quot;keyvault&quot; {
  
  Instance module.redacted.module.keyvault.azurerm_key_vault.keyvault data could
  not be decoded from the state: unsupported attribute &quot;sku&quot;.
  </code></pre>
  <p>My state file is in Azure storage. When looking into the state file we see the problem:</p>
  <pre><code>    {
        &quot;module&quot;: &quot;module.redacted.module.keyvault&quot;,
        &quot;mode&quot;: &quot;managed&quot;,
        &quot;type&quot;: &quot;azurerm_key_vault&quot;,
        &quot;name&quot;: &quot;keyvault&quot;,
        &quot;provider&quot;: &quot;module.redacted.provider.azurerm&quot;,
        &quot;instances&quot;: [
          {
         ...
              &quot;sku&quot;: [
                {
                  &quot;name&quot;: &quot;standard&quot;
                }
              ],
              &quot;sku_name&quot;: &quot;standard&quot;,
        ....
  </code></pre>
  <p>The newest way to define the sku for keyvault is using the &quot;sku_name&quot; attribute. But the old way has stuck into the state file and is now causing problems.</p>
  <p>What is the preferred way to upgrade the provider so that the state file is also cleared up? Or is this something that has to be done manually?</p>