Remove method removeLastPatchSetId() from Change.

Instead, use the patchSet prior to the current patchSet.

This is part of the code cleanup to remove the nbrPatchSets field.

Change-Id: I7355aac57a6959fd145957c2d874a69c29e19c87

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java

@@ -482,15 +482,6 @@ public final class Change {
     ++nbrPatchSets;
   }
 
-  /**
-   * Reverts to an older PatchSet id within this change.
-   * <p>
-   * <b>Note: This makes the change dirty. Call update() after.</b>
-   */
-  public void removeLastPatchSetId() {
-    --nbrPatchSets;
-  }
-
   public void updateNumberOfPatchSets(int max) {
     nbrPatchSets = Math.max(nbrPatchSets, max);
   }