[SYCL][Graph] Remove outdated known issue (#18482)

This note on L0 implementation known issues doesn't exist with out
immediate append path in the L0 adapter.

Author: EwanC

sycl/doc/extensions/experimental/sycl_ext_oneapi_graph.asciidoc

@@ -2476,9 +2476,6 @@ if used in application code.
 
 . Using reductions in a graph node.
 . Using sycl streams in a graph node.
-. Synchronization between multiple executions of the same command-buffer
-  must be handled in the host for level-zero backend, which may involve
-  extra latency for subsequent submissions.
 
 == Revision History