The 7.7k-line qemu-wasm patch was really a fork, so vendor it as a submodule
(pinned at the xteink QEMU fork) and build it directly. Removes the
clone/commit-check/patch/reset machinery, the redundant web-dev/patch targets,
and 0002-qemu-wasm.patch. Editing third_party/qemu now recompiles incrementally
via plain `make web`. Native build keeps 0001-xteink-machine.patch.
