Revert "[Collective][PR 4/6] NCCL Communicator caching and preliminary stream management (ray-project#13030)"

This reverts commit ed6b212.

Author: fishbone

python/ray/util/collective/__init__.py

@@ -1,15 +1,11 @@
-from ray.util.collective.collective import nccl_available, gloo_available, \
+from ray.util.collective.collective import nccl_available, mpi_available, \
     is_group_initialized, init_collective_group, destroy_collective_group, \
-    declare_collective_group, get_rank, get_world_size, allreduce, \
-    allreduce_multigpu, barrier, reduce, reduce_multigpu, broadcast, \
-    broadcast_multigpu, allgather, allgather_multigpu, reducescatter, \
-    reducescatter_multigpu, send, send_multigpu, recv, recv_multigpu
+    get_rank, get_world_size, allreduce, barrier, reduce, broadcast, \
+    allgather, reducescatter, send, recv
 
 __all__ = [
-    "nccl_available", "gloo_available", "is_group_initialized",
-    "init_collective_group", "destroy_collective_group",
-    "declare_collective_group", "get_rank", "get_world_size", "allreduce",
-    "allreduce_multigpu", "barrier", "reduce", "reduce_multigpu", "broadcast",
-    "broadcast_multigpu", "allgather", "allgather_multigpu", "reducescatter",
-    "reducescatter_multigpu", "send", "send_multigpu", "recv", "recv_multigpu"
+    "nccl_available", "mpi_available", "is_group_initialized",
+    "init_collective_group", "destroy_collective_group", "get_rank",
+    "get_world_size", "allreduce", "barrier", "reduce", "broadcast",
+    "allgather", "reducescatter", "send", "recv"
 ]