Fix deleteSNMPClient method in Unit Test file

The previous method can only delete one piece of data, and if the
last piece of data is deleted, an error will be reported and the UT
will fail.

Tested: UT passed.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: If1e0b4170a0a58fb30d4e28c55fed68b0d0f5e28
2 files changed