refactor: remove duplicated cgo/ and mobile/ wrappers

Finishes the h2.core/libh2 separation started in
flows/sdd-h2-libh2-separation/ (2026-05-16). Both directories were
byte-identical copies of libh2/wrappers/cgo/ and libh2/mobile/.

libh2/wrappers/cgo/go.mod already imports github.com/vpnclient/https-vpn,
so libh2 is the wrapper layer over h2.core; the copies here are
migration leftovers. Verified neither dir is imported anywhere inside
the https-vpn module (no refs to https-vpn/cgo or https-vpn/mobile).

No core logic changed — only removal of duplicated wrapper directories.
h2.core keeps pure core + CLI (core/, crypto/, transport/, cmd/https-vpn/).

Author: Arjuna (PrabhuArjun)