Revert "[lldb] Fix data race in ConnectionFileDescriptor"

This reverts commit 0bdbe7b because it
broke the bots.

Author: JDevlieghere

lldb/include/lldb/Host/posix/ConnectionFileDescriptorPosix.h

@@ -131,7 +131,7 @@ class ConnectionFileDescriptor : public Connection {
   lldb::IOObjectSP m_io_sp;
 
   Pipe m_pipe;
-  mutable std::recursive_mutex m_mutex;
+  std::recursive_mutex m_mutex;
   std::atomic<bool> m_shutting_down; // This marks that we are shutting down so
                                      // if we get woken up from
   // BytesAvailable to disconnect, we won't try to read again.

lldb/source/Host/posix/ConnectionFileDescriptorPosix.cpp

@@ -118,7 +118,6 @@ void ConnectionFileDescriptor::CloseCommandPipe() {
 }
 
 bool ConnectionFileDescriptor::IsConnected() const {
-  std::lock_guard<std::recursive_mutex> guard(m_mutex);
   return m_io_sp && m_io_sp->IsValid();
 }