don't support discarding staged lines

Author: jdgarcia

Diff for: lib/repository.js

@@ -1550,18 +1550,16 @@ Repository.prototype.stageLines =
 };
 
 /**
- * Discard line selection of a specified file
+ * Discard line selection of a specified file.
+ * Assumes selected lines are unstaged.
  *
  * @async
  * @param {String} filePath The relative path of this file in the repo
  * @param {Array} selectedLines The array of DiffLine objects
  *                            selected for discarding
- * @param {Boolean} isStaged Are the selected lines currently staged
  * @return {Number} 0 or an error code
  */
-Repository.prototype.discardLines =
-  function(filePath, selectedLines, isSelectionStaged) {
-
+Repository.prototype.discardLines = function(filePath, selectedLines) {
   var repo = this;
   var fullFilePath = path.join(repo.workdir(), filePath);
   var index;
@@ -1576,11 +1574,11 @@ Repository.prototype.discardLines =
     .then(function(content) {
       originalContent = content;
 
-      return getPathHunks(repo, index, filePath, isSelectionStaged);
+      return getPathHunks(repo, index, filePath, false);
     })
     .then(function(hunks) {
       return applySelectedLinesToTarget(
-        originalContent, selectedLines, hunks, isSelectionStaged, true
+        originalContent, selectedLines, hunks, false, true
       );
     })
     .then(function(newContent) {