translate-c: remove concept of "translate mode"

[hryx]

(Please feel free to add a more thorough description)

From conversations on IRC:

20:25 <hryx> what's the TLDR difference between include mode and -c mode?
20:26 <andrewrk> the idea was that in -c mode, you're translating a C project, so non-static functions should be `export` because that's what -c would do
20:26 <andrewrk> but in #include mode, it's like you just want to call the functions
20:26 <andrewrk> now that I'm thinking about it again though, I don't think there should be a difference
20:27 <andrewrk> because if you were to #include a non-static function in C, it would get exported. so the @cImport equivalent of that would be indeed, creating an export function and translating its definition
20:27 <andrewrk> so thinking about it again, I don't see why there needs to be 2 modes

This conversation resulted from work on #2569 .

[FireFox317]

This shouldn't be closed right? @Vexu reverted the change in his PR.

[Vexu]

Only in stage 1, stage 2 no longer has translate mode.

[FireFox317]

Ah, I see. Nice!

[andrewrk]

It's fine to be closed because once self hosted translate-c is caught up, we can just delete the C++ implementation