revert "compiler: packed structs cache bit offsets"

This is mostly a revert of a7088fd9a3edb037f0f51bb402a3c557334634f3.
Measurement revealed the commit actually regressed performance.
c08c0fc6edAndrew Kelley committed on 9/24/2023, 9:37:36 PMparenta7088fd
9 files changedLine totals unavailable