Remove redundant 'private' modifier on constructors

Enum constructors are by default private, so it is not necessary
to explicitly declare them as so.

Change-Id: I871a84ef4950882a27b1d808e68af588a66fbdea

gerrit-server/src/main/java/com/google/gerrit/server/change/ArchiveFormat.java

@@ -31,7 +31,7 @@ public enum ArchiveFormat {
   private final ArchiveCommand.Format<?> format;
   private final String mimeType;
 
-  private ArchiveFormat(String mimeType, ArchiveCommand.Format<?> format) {
+  ArchiveFormat(String mimeType, ArchiveCommand.Format<?> format) {
     this.format = format;
     this.mimeType = mimeType;
     ArchiveCommand.registerFormat(name(), format);

gerrit-server/src/main/java/com/google/gerrit/server/change/GetDiff.java

@@ -403,7 +403,7 @@ public class GetDiff implements RestReadView<FileResource> {
 
     private final DiffPreferencesInfo.Whitespace whitespace;
 
-    private IgnoreWhitespace(DiffPreferencesInfo.Whitespace whitespace) {
+    IgnoreWhitespace(DiffPreferencesInfo.Whitespace whitespace) {
       this.whitespace = whitespace;
     }
   }

gerrit-server/src/main/java/com/google/gerrit/server/git/strategy/CommitMergeStatus.java

@@ -59,7 +59,7 @@ public enum CommitMergeStatus {
 
   private String message;
 
-  private CommitMergeStatus(String message) {
+  CommitMergeStatus(String message) {
     this.message = message;
   }
 

gerrit-server/src/main/java/com/google/gerrit/server/notedb/ReviewerStateInternal.java

@@ -49,7 +49,7 @@ public enum ReviewerStateInternal {
   private final FooterKey footerKey;
   private final ReviewerState state;
 
-  private ReviewerStateInternal(FooterKey footerKey, ReviewerState state) {
+  ReviewerStateInternal(FooterKey footerKey, ReviewerState state) {
     this.footerKey = footerKey;
     this.state = state;
   }