LU-6606 tests: delete memory limit from obdfilter-survey

LU-6606 tests: delete memory limit from obdfilter-survey

This limit prevents to do enough load on newer HW, and have no
relation to current Lustre code. It is safe to remove this limit.

For disk usage the echo_client_brw_ioctl() limit the npages to
PTLRPC_MAX_BRW_SIZE>>PAGE_SHIFT. The total transfer is divided on
small portion with ptlrpc transfer size. Echo client will return
ENOMEM for bad memory allocation. And obdfilter-survey .detail file
will have the next error message
error: test_brw-1: #1 - Cannot allocate memory on write

Signed-off-by: Alexander Boyko <alexander.boyko@seagate.com>
Xyratex-bug-id: MRP-1642
Change-Id: I83d5b811cfa34dd3ec60fb670e595af193495b1c
Reviewed-on: http://review.whamcloud.com/14823
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>