Revert "ARM: Reimplement the UnsafeCASObject intrinsic."

This reverts commit 1bf0b7ad2fc6ba0cc51d0df2890f9f2d0b05b32b.

Reason for revert: The introspection entrypoint would read the
destination register from the wrong bits.

Bug: 36141117
Change-Id: I67c40ba9fb5a834fc5565149269d66a716438e9b
3 files changed