Remove test_stream_struct_write test (#825)

Test has been commented out.
This is effecting clang-format checks in the file.
Removing test as it is not in use.

Change-Id: Ic9a7ab68a514fa6dc01e4d86a7bda1a9856a75e8
Signed-off-by: Ellen Norris-Thompson <ellen.norris-thompson@arm.com>