Turn off kcov on a test that hit kcov#339

Our current version of kcov on bionic has a bug
SimonKagstrom/kcov#339
that generatues spurious failures based on the bitwise contents of
target binaries.  Temporarily deactivate kcov testing of this test to avoid
one such spurious failure.

systems/controllers/BUILD.bazel

@@ -275,6 +275,8 @@ drake_cc_googletest(
 drake_cc_googletest(
     name = "setpoint_test",
     srcs = ["test/setpoint_test.cc"],
+    # TODO(ggould-tri) This test hit kcov#339; untag when we have kcov>=40.
+    tags = ["no_kcov"],
     deps = [
         ":setpoint",
         "//common/test_utilities:eigen_matrix_compare",