tests: Remove problematic but questionably useful part of ovsdb-server test.

tests: Remove problematic but questionably useful part of ovsdb-server test.

The test "ovsdb-server combines updates on backlogged connections" first
checks that ovsdb-server can combine transactions, and then checks that
it can keep them separate.  The latter part is hard to force because it
requires making sure that the socket buffer never fills up, and it also
isn't a very useful test (it doesn't check for any kind of correctness).
Therefore, this commit removes it.

Reported-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Acked-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Ben Pfaff <blp@nicira.com>