Can we remove extra curly braces in -verify diagnostics?

This came up during discussion of https://github.com/llvm/llvm-project/pull/179835/ where the grammar for verify directives is:
```
`directive`
`prefix` ``-`` `diagnostic-kind` `regex-match`:sub:`opt` `diagnostic-loc`:sub:`opt` `quantifier`:sub:`opt` ``{{`` `delimiter-open`:sub:`opt` `diagnostic-text` `delimiter-close`:sub:`opt` ``}}``
```
Do we need the delimiter-open and delimiter-close to be supported? That allows for `// expected-error {{{{dfdfgdfg}}}}` but do the extra curlies *do* anything? I don't think so, this seems like an artifact of the original implementation. Assigning to @endilll for investigation.