ZOOKEEPER-4294: Remove unused IOException on FileSnap#findNValidSnapshots

Author: ruanwenjun <wenjun@apache.org>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, maoling <maoling@apache.org>

Closes #1752 from ruanwenjun/dev_wenjun_patch-4294

zookeeper-server/src/main/java/org/apache/zookeeper/server/persistence/FileSnap.java

@@ -139,7 +139,7 @@ public class FileSnap implements SnapShot {
      * find the most recent snapshot in the database.
      * @return the file containing the most recent snapshot
      */
-    public File findMostRecentSnapshot() throws IOException {
+    public File findMostRecentSnapshot() {
         List<File> files = findNValidSnapshots(1);
         if (files.size() == 0) {
             return null;
@@ -157,9 +157,8 @@ public class FileSnap implements SnapShot {
      * @param n the number of most recent snapshots
      * @return the last n snapshots (the number might be
      * less than n in case enough snapshots are not available).
-     * @throws IOException
      */
-    protected List<File> findNValidSnapshots(int n) throws IOException {
+    protected List<File> findNValidSnapshots(int n) {
         List<File> files = Util.sortDataDir(snapDir.listFiles(), SNAPSHOT_FILE_PREFIX, false);
         int count = 0;
         List<File> list = new ArrayList<File>();

zookeeper-server/src/main/java/org/apache/zookeeper/server/persistence/FileTxnSnapLog.java

@@ -561,9 +561,8 @@ public class FileTxnSnapLog {
      * @param n the number of recent valid snapshots
      * @return the list of n recent valid snapshots, with
      * the most recent in front
-     * @throws IOException
      */
-    public List<File> findNValidSnapshots(int n) throws IOException {
+    public List<File> findNValidSnapshots(int n) {
         FileSnap snaplog = new FileSnap(snapDir);
         return snaplog.findNValidSnapshots(n);
     }