Remove support for `quotemark` option since there is a bug

[Glavin001]

See https://github.com/Unibeautify/beautifier-prettydiff/blob/master/src/options.ts#L37

Critical bug: prettydiff/prettydiff#508

[prettydiff]

This is mostly resolved in the latest version of Pretty Diff I just published. I just noticed that support appears to be missing from markup code. I will be looking into this tonight. I already have an issue open: Unibeautify/sparser#64