--decompress does more than just desubroutinize

I noticed that when the "-d" (or "--decompress") option is provided to compreffor, then the output file size gets much smaller.
The reason is that the `fontTools.subset.Options` include a lot more optimizations which are performed by default, besides the requested desubroutinization.
From a user point of view, the "decompress" option should only desubroutinize the CFF table, and not also perform the rest of the optimizations.
I think the best way to address this would be to make the desubroutinization independent from the fontTools.subset module, as @behdad already noted here https://github.com/behdad/fonttools/issues/283.