[objcopy][MachO] Revert special handling of encryptable binaries (#144058)
Code originally added in #120995 and later corrected in #130517 but
apparently still not correct according to #141494 and
rust-lang/rust#141913.
Revert the special handling because the test written in #120995 and
#130517 still passes without those changes. Kept the test and improved
it with a `__DATA` section to keep the current behaviour checked in case
other changes modify the behaviour and break this edge case.
(cherry picked from commit a0662ceba83cf8782da4047b8ee6d175591f168f)