Remove unused context initializer functions

[thomaseizinger]

Fixes #15.

[apoelstra]

lol. now that we've stopped rebasing maybe these will stay gone :)

[thomaseizinger]

lol. now that we've stopped rebasing maybe these will stay gone :)

I wasn't aware! Did functions keep coming back from upstream?

[apoelstra]

These functions existed a very long time ago, in Elements Alpha, before Elements had Confidential Asset support. @sipa and I spent some time in 2016 replacing the precomputation tables in the rangeproof code with non-precomp code, since our constant H generator was replaced by a variable asset generator as part of CA. But we forgot to remove the two precomputation functions from the header.

We noticed this some years later, and I swear I remember deleting them after that, but at some point a few rebases had gone by and I saw that they'd returned. This may have happened more than once, I don't remember now.

I deleted them again as part of #108 but you beat me to it :)

[apoelstra]

lol, I realize that the rangeproof sign/verify functions still talk about needing a context "initialized for rangeproof and pedersen commitment"