Move over to using JniLoader.jniEnabled to simplify code.

RELNOTES:
PiperOrigin-RevId: 279092981
diff --git a/src/main/java/com/google/devtools/build/lib/platform/SleepPreventionModule.java b/src/main/java/com/google/devtools/build/lib/platform/SleepPreventionModule.java
index bf2735c..a8ad277 100644
--- a/src/main/java/com/google/devtools/build/lib/platform/SleepPreventionModule.java
+++ b/src/main/java/com/google/devtools/build/lib/platform/SleepPreventionModule.java
@@ -43,22 +43,16 @@
     public static native int popDisableSleep();
   }
 
-  private final Boolean jniEnabled;
-
-  public SleepPreventionModule() {
-    this.jniEnabled = !"0".equals(System.getProperty("io.bazel.EnableJni"));
-  }
-
   @Override
   public void beforeCommand(CommandEnvironment env) throws AbruptExitException {
-    if (jniEnabled) {
+    if (JniLoader.jniEnabled()) {
       SleepPrevention.pushDisableSleep();
     }
   }
 
   @Override
   public void afterCommand() throws AbruptExitException {
-    if (jniEnabled) {
+    if (JniLoader.jniEnabled()) {
       SleepPrevention.popDisableSleep();
     }
   }