docs: fix the statements for setting up the trtllm NIXL backends (#5763)

docs/backends/trtllm/kv-cache-transfer.md

@@ -30,43 +30,11 @@ By default, TensorRT-LLM uses **NIXL** (NVIDIA Inference Xfer Library) with UCX
 
 ### Specify Backends for NIXL
 
-NIXL supports multiple communication backends that can be configured via environment variables. By default, UCX is used if no backends are explicitly specified.
-
-**Environment Variable Format:**
-```bash
-DYN_KVBM_NIXL_BACKEND_<BACKEND>=<value>
-```
-
-**Supported Backends:**
-- `UCX` - Unified Communication X (default)
-- `GDS` - GPU Direct Storage
-
-**Examples:**
-```bash
-# Enable UCX backend (default behavior)
-export DYN_KVBM_NIXL_BACKEND_UCX=true
-
-# Enable GDS backend
-export DYN_KVBM_NIXL_BACKEND_GDS=true
-
-# Enable multiple backends
-export DYN_KVBM_NIXL_BACKEND_UCX=true
-export DYN_KVBM_NIXL_BACKEND_GDS=true
-
-# Explicitly disable a backend
-export DYN_KVBM_NIXL_BACKEND_GDS=false
-```
-
-**Valid Values:**
-- `true`, `1`, `on`, `yes` - Enable the backend
-- `false`, `0`, `off`, `no` - Disable the backend
-
-> [!Note]
-> If no `DYN_KVBM_NIXL_BACKEND_*` environment variables are set, UCX is used as the default backend.
+TensorRT-LLM supports two NIXL communication backends: UCX and LIBFABRIC. By default, UCX is used if no backend is explicitly specified. Dynamo currently only supports the UCX backend, as LIBFABRIC support is still a work in progress. Please do not change the NIXL backend in the Dynamo runtime image.
 
 ## Alternative Method: UCX
 
 TensorRT-LLM can also leverage **UCX** (Unified Communication X) directly for KV cache transfer between prefill and decode workers. To enable UCX as the KV cache transfer backend, set `cache_transceiver_config.backend: UCX` in your engine configuration YAML file.
 
 > [!Note]
-> The environment variable `TRTLLM_USE_UCX_KV_CACHE=1` with `cache_transceiver_config.backend: DEFAULT` does not enable UCX. You must explicitly set `backend: UCX` in the configuration.
+> The environment variable `TRTLLM_USE_UCX_KVCACHE=1` with `cache_transceiver_config.backend: DEFAULT` does not enable UCX. You must explicitly set `backend: UCX` in the configuration.