remove callback from createCommitWithSignature

Author: Dan Butvinik

lib/repository.js

@@ -642,8 +642,7 @@ Repository.prototype.createCommitWithSignature = function(
     tree,
     parents,
     signature_field,
-    onSignature,
-    callback) {
+    onSignature) {
 
   var repo = this;
   var promises = [];
@@ -687,7 +686,7 @@ Repository.prototype.createCommitWithSignature = function(
       commit_content,
       signature,
       signature_field);
-  }, callback);
+  });
 };
 
 /**