Remove the unnecessary sleep in MachProcess::AttachForDebug. The
preceding comment makes it seem like it's necessary for synchronization,
though I don't believe that's the case (see below), and even if it were,
sleeping is not a reliable way to achieve that.
The reason I don't believe it's necessary is because after we return, we
synchronize with the exception thread on a state change. The latter will
call and update the process state, which is exactly what we synchronize
on. I was able to verify that this is the first time we change the
process state: i.e., `GetState` doesn't return a different value before
and after the sleep.
On top of that, there are 3 more places where we call ptrace attach
(`PosixSpawnChildForPTraceDebugging`, `SBLaunchForDebug`, and
`BoardServiceLaunchForDebug`) where we don't sleep.
rdar://163952037
fa83723bbe