Comment out failing valgrind object manager test.

[robertnishihara]

See #3979.

[pcmoritz]

If we want a quick fix for this, reverting the inline object pr until the valgrind issue is fixed seems the better solution to me.

Event better let's try to fix the valgrind issue.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/Ray-PRB/11656/
Test PASSed.

[guoyuhong]

As described in #4007:

object_manager_test.cc failed since 3756 when VALGRIND is used. However, this test works fine in none-valgrind case. I increased the data size above the inline object threshold and the test passed. Maybe the owner needs to take a look at why the valgrind test fails when inline object is enabled.