Remove `$` from face names for interoperability with treesit

`$` is fine as a Lisp symbol, but there is a problem with compatibility with treesit, so we will rename them.

 * `php-$this` → `php-this`
 * `php-$this-sigil` → `php-this-sigil`

refs https://github.com/emacs-php/php-ts-mode/pull/68