IO-689: FileUtils: Remove Instant->ZonedDateTime->Instant round-trip

This to/from round-trip conversion has no effect on the value of the
Instant.

Author: aherbert

src/changes/changes.xml

@@ -59,6 +59,9 @@ The <action> type attribute can be add,update,fix,remove.
       <action dev="ggregory" type="update" due-to="Gary Gregory">
         Update commons.jacoco.version 0.8.5 to 0.8.6 (Fixes Java 15 builds).
       </action>
+      <action issue="IO-689" dev="aherbert" type="fix" due-to="Uwe Schindler">
+        FileUtils: Remove Instant->ZonedDateTime->Instant round-trip.
+      </action>
     </release>
     <!-- The release date is the date RC is cut -->
     <release version="2.8.0" date="2020-09-05" description="Java 8 required.">

src/main/java/org/apache/commons/io/FileUtils.java

@@ -1787,7 +1787,7 @@ public static boolean isFileNewer(final File file, final File reference) {
      */
     public static boolean isFileNewer(final File file, final Instant instant) {
         Objects.requireNonNull(instant, "instant");
-        return isFileNewer(file, instant.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli());
+        return isFileNewer(file, instant.toEpochMilli());
     }
 
     /**
@@ -1955,7 +1955,7 @@ public static boolean isFileOlder(final File file, final File reference) {
      */
     public static boolean isFileOlder(final File file, final Instant instant) {
         Objects.requireNonNull(instant, "instant");
-        return isFileOlder(file, instant.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli());
+        return isFileOlder(file, instant.toEpochMilli());
     }
 
     /**