Remove mention of -Xincremental from CodeServer options' help

Follow-up to 6c2cc42ecfe8c4640f71998c5b7cef447ebae351 which removed
the -Xincremental flag but forgot to update this small piece of doc
referencing it.

Change-Id: Iec47df6d53e15b8840f4c18a0a301e49d758cf17

dev/codeserver/java/com/google/gwt/dev/codeserver/Options.java

diff --git a/dev/codeserver/java/com/google/gwt/dev/codeserver/Options.java b/dev/codeserver/java/com/google/gwt/dev/codeserver/Options.java
index b7454d1..42732ee 100644
--- a/dev/codeserver/java/com/google/gwt/dev/codeserver/Options.java
+++ b/dev/codeserver/java/com/google/gwt/dev/codeserver/Options.java
@@ -335,8 +335,7 @@
 
     @Override
     public String getPurposeSnippet() {
-      return "Compiles faster by creating/reusing a JS file per class. "
-          + "Can't be used with -Xincremental.";
+      return "Compiles faster by creating/reusing a JS file per class.";
     }
 
     @Override