[lldb] Remove unused GDBRemoteCommunicationClient::SendAttach function

[DavidSpickett]

Asking for review to double check. Nothing in lldb upstream calls this and I think that's because we switched to a style where we ask to attach then have a callback that will tell us once it's done.

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h

public:
   int SendEnvironmentPacket(char const *name_equal_value);
   int SendEnvironment(const Environment &env);
 
   int SendLaunchArchPacket(const char *arch);
 
   int SendLaunchEventDataPacket(const char *data,
                                 bool *was_supported = nullptr);
 
-  /// Sends a "vAttach:PID" where PID is in hex.
-  ///
-  /// \param[in] pid
-  ///     A process ID for the remote gdb server to attach to.
-  ///
-  /// \param[out] response
-  ///     The response received from the gdb server. If the return
-  ///     value is zero, \a response will contain a stop reply
-  ///     packet.
-  ///
-  /// \return
-  ///     Zero if the attach was successful, or an error indicating
-  ///     an error code.
-  int SendAttach(lldb::pid_t pid, StringExtractorGDBRemote &response);
-
   /// Sends a GDB remote protocol 'I' packet that delivers stdin
   /// data to the remote process.
   ///
   /// \param[in] data
   ///     A pointer to stdin data.
   ///
   /// \param[in] data_len
   ///     The number of bytes available at \a data.

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp

if (SendPacketAndWaitForResponse("qHostInfo", response) ==
         if (!distribution_id.empty())
           m_host_arch.SetDistributionId(distribution_id.c_str());
       }
     }
   }
   return m_qHostInfo_is_valid == eLazyBoolYes;
 }
 
-int GDBRemoteCommunicationClient::SendAttach(
-    lldb::pid_t pid, StringExtractorGDBRemote &response) {
-  if (pid != LLDB_INVALID_PROCESS_ID) {
-    char packet[64];
-    const int packet_len =
-        ::snprintf(packet, sizeof(packet), "vAttach;%" PRIx64, pid);
-    UNUSED_IF_ASSERT_DISABLED(packet_len);
-    assert(packet_len < (int)sizeof(packet));
-    if (SendPacketAndWaitForResponse(packet, response) ==
-        PacketResult::Success) {
-      if (response.IsErrorResponse())
-        return response.GetError();
-      return 0;
-    }
-  }
-  return -1;
-}
-
 int GDBRemoteCommunicationClient::SendStdinNotification(const char *data,
                                                         size_t data_len) {
   StreamString packet;
   packet.PutCString("I");
   packet.PutBytesAsRawHex8(data, data_len);
   StringExtractorGDBRemote response;
   if (SendPacketAndWaitForResponse(packet.GetString(), response) ==
       PacketResult::Success) {