selftests: mptcp: simult_flows: disable 'flaky' mark

Thanks to recent commits removing high bufferbloat in this case, the
"unbalanced bwidth" subtest has a more stable transfer.

Thanks to that, it looks like the test is no longer flaky (hopefully).

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Author: matttbe

tools/testing/selftests/net/mptcp/simult_flows.sh

@@ -307,7 +307,7 @@ run_test 10 10 0 0  20 20 "balanced bwidth"
 run_test 10 10 1 25 20 50 "balanced bwidth with unbalanced delay"
 
 # we still need some additional infrastructure to pass the following test-cases
-MPTCP_LIB_SUBTEST_FLAKY=1 run_test 10 3 0 0  30 20 "unbalanced bwidth"
+run_test 10 3 0 0  30 20 "unbalanced bwidth"
 run_test 10 3 1 25 40 30 "unbalanced bwidth with unbalanced delay"
 run_test 10 3 25 1 50 30 "unbalanced bwidth with opposed, unbalanced delay"