Remove mocha.opts from supported filetypes list

Technically, this is a filetype recognised by the "Options list" grammar
(which is derived straight from POSIX shell-option syntax). In addition,
Mocha deprecated the `mocha.opts` format in v6.0.0, making this filetype
even less worthy of an advertisement (source: mochajs/mocha#3556).

README.md

@@ -65,7 +65,6 @@ Supported formats
 * [ ] [Hunspell dictionaries](https://github.com/hunspell/hunspell/blob/master/man/hunspell.5)
 * [x] [M4/Autotools](http://wolfram.schneider.org/bsd/7thEdManVol2/m4/m4.pdf)
 * [x] [`man.conf`](https://man.openbsd.org/man.conf.5)
-* [x] [`mocha.opts`](https://mochajs.org/#mochaopts)
 * [x] [NEON](https://ne-on.org/)
 * [x] [NWScript](https://en.wikipedia.org/wiki/NWScript)
 * [x] [Object Data Instance Notation](https://git.io/JvetL)