Make OS/2 table optional

[specious]

The code throws an error if the OS/2 table is missing in the source font.

In Apple's reference manual for TrueType fonts, the OS/2 table is listed as an optional table.

The OS/2 table reference says:

The 'OS/2' table consists of a set of metrics that are required by Windows. It is not fully used by Apple platforms.

It also says:

A number of fields in the 'OS/2' table replicate data found elsewhere in the font; most notably, the various ascent and descent fields mirror some of the contents of the horizontal header table. The macOS derives ascent and descent information from the latter; Windows from the former.

It seems that while the OS/2 table might play a role in a system font, it may not be necessary in a web font.

Is there a really good reason why a font should not pass without an OS/2 table? Perhaps it could produce a warning rather than an error.

[specious]

To provide some context, I've got a use case where my goal is to produce web fonts with the smallest possible footprint.

I can remove optional tables with ftCLI before passing them through fontmin (which uses fonteditor-core) to remove unused glyphs from the fonts.

However, if I delete the OS/2 table, which serves no purpose in my use case, the fonts will not pass.