resource/aws_dynamodb_table: Skip ResourceNotFoundException during de…

…letion (#11692)

Previously in the acceptance testing:

```
--- FAIL: TestAccAWSDynamoDbGlobalTable_multipleRegions (67.39s)
    testing.go:701: Error destroying resource! WARNING: Dangling resources
        may exist. The full state and error is shown below.

        Error: errors during apply: error deleting DynamoDB Table (tf-acc-test-tyuvv): Error deleting DynamoDB table: ResourceNotFoundException: Requested resource not found: Table: tf-acc-test-tyuvv not found
```

The prior code would wrap the `awserr.Error` in a `fmt.Errorf()` which meant the error was returned by value. The calling code already handles the error message context, so we remove the error wrapping so consumers can work with the AWS error type correctly. Another solution here would be instead using the Go 1.13 `%w` format verb, which will be part of a future linting check.

Output from acceptance testing:

```
--- PASS: TestAccAWSDynamoDbGlobalTable_basic (86.21s)
--- PASS: TestAccAWSDynamoDbGlobalTable_multipleRegions (106.17s)

--- PASS: TestAccAWSDynamoDbTable_attributeUpdate (463.78s)
--- PASS: TestAccAWSDynamoDbTable_attributeUpdateValidation (6.14s)
--- PASS: TestAccAWSDynamoDbTable_basic (27.57s)
--- PASS: TestAccAWSDynamoDbTable_BillingMode_GSI_PayPerRequestToProvisioned (57.72s)
--- PASS: TestAccAWSDynamoDbTable_BillingMode_GSI_ProvisionedToPayPerRequest (1149.43s)
--- PASS: TestAccAWSDynamoDbTable_BillingMode_PayPerRequestToProvisioned (45.62s)
--- PASS: TestAccAWSDynamoDbTable_BillingMode_ProvisionedToPayPerRequest (1325.53s)
--- PASS: TestAccAWSDynamoDbTable_disappears (19.40s)
--- PASS: TestAccAWSDynamoDbTable_disappears_PayPerRequestWithGSI (100.90s)
--- PASS: TestAccAWSDynamoDbTable_enablePitr (133.02s)
--- PASS: TestAccAWSDynamoDbTable_encryption (62.77s)
--- PASS: TestAccAWSDynamoDbTable_extended (195.41s)
--- PASS: TestAccAWSDynamoDbTable_gsiUpdateCapacity (56.73s)
--- PASS: TestAccAWSDynamoDbTable_gsiUpdateNonKeyAttributes (157.72s)
--- PASS: TestAccAWSDynamoDbTable_gsiUpdateOtherAttributes (465.18s)
--- PASS: TestAccAWSDynamoDbTable_streamSpecification (67.08s)
--- PASS: TestAccAWSDynamoDbTable_streamSpecificationValidation (4.85s)
--- PASS: TestAccAWSDynamoDbTable_tags (36.51s)
--- PASS: TestAccAWSDynamoDbTable_Ttl_Disabled (41.27s)
--- PASS: TestAccAWSDynamoDbTable_Ttl_Enabled (29.97s)
```

aws/resource_aws_dynamodb_table.go

@@ -694,13 +694,12 @@ func deleteAwsDynamoDbTable(tableName string, conn *dynamodb.DynamoDB) error {
 		}
 		return nil
 	})
+
 	if isResourceTimeoutError(err) {
 		_, err = conn.DeleteTable(input)
 	}
-	if err != nil {
-		return fmt.Errorf("Error deleting DynamoDB table: %s", err)
-	}
-	return nil
+
+	return err
 }
 
 func waitForDynamodbTableDeletion(conn *dynamodb.DynamoDB, tableName string, timeout time.Duration) error {