Autofix for the deprecated interpolation rule produces ambiguous attribute keys

[wata727]

Follow up of #184

The terraform_deprecated_interpolation rule may produce ambiguous attribute keys if the map key contains a deprecated interpolation.

$ cat main.tf
variable "foo" {}

locals {
  tags = {
    "${var.foo}" = "bar"
  }
}
$ terraform validate
Success! The configuration is valid.

$ tflint --fix --only terraform_deprecated_interpolation
1 issue(s) found:

Warning: [Fixed] Interpolation-only expressions are deprecated in Terraform v0.12.14 (terraform_deprecated_interpolation)

  on main.tf line 5:
   5:     "${var.foo}" = "bar"

Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.7.0/docs/rules/terraform_deprecated_interpolation.md

$ cat main.tf
variable "foo" {}

locals {
  tags = {
    var.foo = "bar"
  }
}
$ terraform validate
terraform validate
╷
│ Error: Ambiguous attribute key
│
│   on main.tf line 5, in locals:
│    5:     var.foo = "bar"
│
│ If this expression is intended to be a reference, wrap it in parentheses. If it's instead intended as a literal name containing periods, wrap it in quotes to create
│ a string literal.

This is probably an autofix bug; it should produce (var.foo). Instead of always removing "${}", we should probably implement context-sensitive autofix.