Don't enable async mode at the end of target ::resume methods.

Now that target_resume always enables async mode after target::resume
returns, these calls are redundant.

The other place that target resume methods are invoked outside of
target_resume are as the beneath target in record_full_wait_1.  In
this case, async mode should already be enabled when supported by the
target before the resume method is invoked due to the following:

  In general, targets which support async mode run as async until
  ::wait returns TARGET_WAITKIND_NO_RESUMED to indicate that there are
  no unwaited for children (either they have exited or are stopped).
  When that occurs, the loop in wait_one disables async mode.  Later
  if a stopped child is resumed, async mode is re-enabled in
  do_target_resume before waiting for the next event.

  In the case of record_full_wait_1, this function is invoked from the
  ::wait target method when fetching an event.  If the underlying
  target supports async mode, then an earlier call to do_target_resume
  to resume the child reporting an event in the loop in
  record_full_wait_1 would have already enabled async mode before
  ::wait was invoked.  In addition, nothing in the code executed in
  the loop in record_full_wait_1 disables async mode.  Async mode is
  only disabled higher in the call stack in wait_one after ::wait
  returns.

  It is also true that async mode can be disabled by an
  INF_EXEC_COMPLETE event passed to inferior_event_handle, but all of
  the places that invoke that are in the gdb core which is "above" a
  target ::wait method.

Note that there is an earlier call to enable async mode in
linux_nat_target::resume.  That call also marks the async event pipe
to report an existing event after enabling async mode, so it needs to
stay.

gdb/linux-nat.c

@@ -1703,9 +1703,6 @@ linux_nat_target::resume (ptid_t ptid, int step, enum gdb_signal signo)
 			   ? strsignal (gdb_signal_to_host (signo)) : "0"));
 
   linux_resume_one_lwp (lp, step, signo);
-
-  if (target_can_async_p ())
-    target_async (1);
 }
 
 /* Send a signal to an LWP.  */

gdb/record-full.c

@@ -1095,11 +1095,6 @@ record_full_target::resume (ptid_t ptid, int step, enum gdb_signal signal)
 
       this->beneath ()->resume (ptid, step, signal);
     }
-
-  /* We are about to start executing the inferior (or simulate it),
-     let's register it with the event loop.  */
-  if (target_can_async_p ())
-    target_async (1);
 }
 
 static int record_full_get_sig = 0;
@@ -2062,11 +2057,6 @@ record_full_core_target::resume (ptid_t ptid, int step,
   record_full_resume_step = step;
   record_full_resumed = 1;
   record_full_execution_dir = ::execution_direction;
-
-  /* We are about to start executing the inferior (or simulate it),
-     let's register it with the event loop.  */
-  if (target_can_async_p ())
-    target_async (1);
 }
 
 /* "kill" method for prec over corefile.  */

gdb/remote.c

@@ -6571,16 +6571,6 @@ remote_target::resume (ptid_t ptid, int step, enum gdb_signal siggnal)
   for (thread_info *tp : all_non_exited_threads (this, ptid))
     get_remote_thread_info (tp)->set_resumed ();
 
-  /* We are about to start executing the inferior, let's register it
-     with the event loop.  NOTE: this is the one place where all the
-     execution commands end up.  We could alternatively do this in each
-     of the execution commands in infcmd.c.  */
-  /* FIXME: ezannoni 1999-09-28: We may need to move this out of here
-     into infcmd.c in order to allow inferior function calls to work
-     NOT asynchronously.  */
-  if (target_can_async_p ())
-    target_async (1);
-
   /* We've just told the target to resume.  The remote server will
      wait for the inferior to stop, and then send a stop reply.  In
      the mean time, we can't start another command/query ourselves