Revert "Add scripts to mount/unmount the Runtime APEX under ART's chroot dir."

This reverts commit 7b7ea7939e2c7d5bffd5ad165d0c2d315c93dd1f.

Reason for revert: These scripts were never used as we ended up using
flattened APEXes on the ART Buildbot instead
(https://android-review.googlesource.com/c/platform/art/+/921093/),
where the "mount" logic is implemented during the device sync step,
and the "unmount" logic is performed as part of the device tear-down
step.

Test: Rely on the ART Buildbot
Bug: 121117762
Bug: 113373927
Bug: 34729697
Change-Id: I0dbd728487172daaa28fa5406c44447d25189119
4 files changed