Bug 40416: updated obfsproxy to 0.0.12

I was not sure about the go_lib_install for https://gitlab.com/yawning/edwards25519-extra.git, as only elligator2 is required.

Also, gobsaes specifies a different commit (51ab0e2deafac1f46c46ad59cf0921be2f180c3d) in its go.mod from the one we are using (fae7ac547cb717d141c433a2a173315e216b64c4). The former is more recent, however both of them compile. For the moment, I kept the one we already had.

ed25519 should be removable now (obfsproxy switched to its fork filippo.io/edwards25519).

This MR fixes #40416 (closed).