build: fix kokoro build (#486)

Author: olavloite

.kokoro/build.sh

@@ -43,8 +43,6 @@ fi
 # otherwise run all the sessions.
 if [[ -n "${NOX_SESSION:-}" ]]; then
     python3 -m nox -s ${NOX_SESSION:-}
-elif [[ "${RUN_COMPLIANCE_TESTS}" -eq "false" ]]; then
-    python3 -m nox -s unit
 else
-    python3 -m nox
+    python3 -m nox -s unit
 fi

.kokoro/presubmit/presubmit.cfg

@@ -1,7 +1 @@
 # Format: //devtools/kokoro/config/proto/build.proto
-
-# Disable system tests.
-env_vars: {
-    key: "RUN_COMPLIANCE_TESTS"
-    value: "false"
-}