[debugserver] Remove unnecessary sleep in MachProcess::AttachForDebug (llvm#166674)

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

Author: JDevlieghere

lldb/tools/debugserver/source/MacOSX/MachProcess.mm

@@ -2853,12 +2853,6 @@ static uint64_t bits(uint64_t value, uint32_t msbit, uint32_t lsbit) {
 
     if (err.Success()) {
       m_flags |= eMachProcessFlagsAttached;
-      // Sleep a bit to let the exception get received and set our process
-      // status
-      // to stopped.
-      ::usleep(250000);
-      DNBLog("[LaunchAttach] (%d) Done napping after ptrace(PT_ATTACHEXC)'ing",
-             getpid());
       DNBLogThreadedIf(LOG_PROCESS, "successfully attached to pid %d", pid);
       return m_pid;
     } else {