message: Remove support for requesting a THINBLOCK via getdata.
  There are no longer any peers on the current bitcoin cash chain
  that could support this feature so it is safe to remove. We now only
  allow THINBLOCK requests via the get_thin p2p message.
diff: @@ -91,8 +91,7 @@ void static ProcessGetData(CNode *pfrom, const Consensus::Params &consensusParam
  {
  return;
  }
  - if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK || inv.type == MSG_THINBLOCK ||
  - inv.type == MSG_CMPCT_BLOCK)
  + if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK || inv.type == MSG_CMPCT_BLOCK)
  {
  auto *mi = LookupBlockIndex(inv.hash);
  if (mi)
  @@ -189,14 +188,6 @@ void static ProcessGetData(CNode *pfrom, const Consensus::Params &consensusParam
  pfrom->blocksSent += 1;
  pfrom->PushMessage(NetMsgType::BLOCK, block);
  }
  - else if (inv.type == MSG_THINBLOCK && pfrom->xVersion.as_u64c(XVer::BU_XTHIN_VERSION) < 2 &&
  - pfrom->ThinBlockCapable())
  - {
  - // TODO: This code path enables backward compatibility for older BU nodes
  - // and can be removed in the future.
  - LOG(THIN, "Sending thinblock via getdata message\n");
  - SendXThinBlock(MakeBlockRef(block), pfrom, inv);
  - }
  else if (inv.type == MSG_CMPCT_BLOCK)
  {
  LOG(CMPCT, "Sending compactblock via getdata message\n");
  @@ -1024,14 +1015,14 @@ bool ProcessMessage(CNode *pfrom, std::string strCommand, CDataStream &vRecv, in
  {
  const CInv &inv = vInv[nInv];
  if (!((inv.type == MSG_TX) || (inv.type == MSG_BLOCK) || (inv.type == MSG_FILTERED_BLOCK) ||
  - (inv.type == MSG_CMPCT_BLOCK) || (inv.type == MSG_THINBLOCK)))
  + (inv.type == MSG_CMPCT_BLOCK)))
  {
  dosMan.Misbehaving(pfrom, 20);
  return error("message inv invalid type = %u", inv.type);
  }
  // Make basic checks
  - if (inv.type == MSG_CMPCT_BLOCK || inv.type == MSG_THINBLOCK)
  + if (inv.type == MSG_CMPCT_BLOCK)
  {
  if (!requester.CheckForRequestDOS(pfrom, chainparams))
  return false;
  