Bug 1607153 - Remove the incorrect extra close of IPC channel client_pipe_. r=froydnj

It's no longer safe to try closing client_pipe_ when the I/O thread is
woken up with data from the child process, because that can race with the
launch thread doing its own close, and it's also unnecessary because of
that other close.  See also bug 1607153 comment #2.

Differential Revision: https://phabricator.services.mozilla.com/D60627

--HG--
extra : moz-landing-system : lando

ipc/chromium/src/chrome/common/ipc_channel_posix.cc

@@ -370,12 +370,6 @@ bool Channel::ChannelImpl::ProcessIncomingMessages() {
     }
     DCHECK(bytes_read);
 
-    if (client_pipe_ != -1) {
-      PipeMap::instance().Remove(pipe_name_);
-      IGNORE_EINTR(close(client_pipe_));
-      client_pipe_ = -1;
-    }
-
     // a pointer to an array of |num_wire_fds| file descriptors from the read
     const int* wire_fds = NULL;
     unsigned num_wire_fds = 0;