Remove unnecessary usage of `new String(...)`

According to Findbugs:

  Using the java.lang.String(String) constructor wastes memory because
  the object so constructed will be functionally indistinguishable from
  the String passed as a parameter.

  Just use the argument String directly.

Change-Id: I85a3fd0b85afcae356181eef3e7262d9bf0fa600

src/main/java/com/googlesource/gerrit/plugins/validators/CommitMessageLengthValidation.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/validators/CommitMessageLengthValidation.java b/src/main/java/com/googlesource/gerrit/plugins/validators/CommitMessageLengthValidation.java
index 9e3876e..ff7f1aa 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/validators/CommitMessageLengthValidation.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/validators/CommitMessageLengthValidation.java
@@ -87,8 +87,8 @@
 
     if (this.maxSubjectLength < commit.getShortMessage().length()) {
       onLineTooLong(id, messages,
-          new String("commit subject >" + this.maxSubjectLength
-              + " characters; use shorter first paragraph"));
+          "commit subject >" + this.maxSubjectLength
+          + " characters; use shorter first paragraph");
     }
 
     int longLineCnt = 0;
@@ -104,9 +104,9 @@
 
     if (longLineCnt > (longLinesThreshold * nonEmptyCnt) / 100) {
       onLineTooLong(id, messages,
-          new String("too many commit message lines longer than "
-              + this.maxLineLength
-              + " characters; manually wrap lines"));
+          "too many commit message lines longer than "
+          + this.maxLineLength
+          + " characters; manually wrap lines");
     }
 
     return messages;