Revert "[ot-shape-normalize] Move buffer out of hb_ot_shape_normalize_context_t"

This reverts commit 8cdbea5580731c2bf66e56bf619c1fbb2978692e.

For some reason this is causing several tests to crash locally for me
(on macOS), see:
https://github.com/harfbuzz/harfbuzz/commit/8cdbea5580731c2bf66e56bf619c1fbb2978692e#commitcomment-55898088
2 files changed