[XLA] Remove a check that verified channel_ids for host send/recv ins…

…tructions were unique.

We can't think of why this check is needed in the first place, and it breaks as soon as one has a host send/recv inside an inner computation in the presence of inlining.

For example, consider the pseudo-code:

```
def f(...):
  send(..., channel_id=42)

def main(...):
  f(...)
  f(...)
```

If we inline `f`, then we now violate that invariant. But inlining is something that should always be safe to do.

PiperOrigin-RevId: 689478598

xla/service/hlo_verifier.cc

@@ -2515,11 +2515,6 @@ absl::Status VerifyChannels(const HloModule& module,
             << "channel " << pair.first
             << " is used for different types of channel instructions";
       }
-      if (sendrecv->is_host_transfer()) {
-        TF_RET_CHECK(instructions.size() == 2)
-            << "channel " << pair.first
-            << " is used for multiple host send/recv instructions";
-      }
     } else {
       for (const HloInstruction* instr : instructions) {
         if (opts.verify_unique_channel_ids) {