Drop phantom fields?

[gcanti]

@sledorze @raveclassic the internals of fp-ts don't rely on the presence on those phantom fields anymore (_A, _L, etc...), do we want to try to remove them and ship version 1.16 in future releases? This would allow to test this change in the wild (and overall it's quite easy to revert in case of issues)

[raveclassic]

Yeah, let's try to drop them. However I won't be able to test the changes in production env/projects soon.

[sledorze]

I can try on our code base this week.
It will surely breaks some stuff.
:)