posenet: switch to @tensorflow/tfjs-backend-wasm

[wacky6]

• Eliminate Dockerfile.full
• Test alpine with beamcoder, canvas, and python libs
• Compare image size, decide whether to merge

WASM processing speed is acceptable. Maybe 2.5x slowdown.

[wacky6]

tfjs-wasm branch confirmed working. ~0.5x speed compared to tfjs-node, 50% shrink in docker image size. May shrink more by bundling python scripts.

[wacky6]

fixed: eaeebd408e72500e39d8631ab468e1324ee4b2d6