HKDF&PBKDF2: Dead write to "extractable" bit during importKey operation

[BenWiederhake]

SubtleCrypto.importKey invokes the algorithm's importKey operation in step 3, and overwrites the [[extractable]] internal slot in step 10, regardless what the algorithm wrote into that slot:

So why does HKDF's importKey operation write false into that slot?

I'm not sure what happened here, and therefore not sure how to resolve this issue:

• Option 1: There's a good reason why it should be [[extractable]] = false;, the key should not be extractable. In this case, SubtleCrypto.importKey must be changed in order to preserve that flag.
• Option 2: It's just a dead write that nobody noticed before. In this case, it might be nice to remove the dead write.

EDIT: Also affects PBKDF2's importKey.

Found while combing through the docs for #376, which I in turn found while implementing this from scratch. Shameless plug: Ladybird :)

[twiss]

Both algorithms say:

2. If extractable is not false, then throw a SyntaxError.

So both options are essentially true: extractable must be false, but also the write is dead and can be removed in favor of the one in importKey() as you noted.