Don't suggest default namespaces.

This just ends adding a lot of `minecraft:` to otherwise short commands.

(cherry picked from commit d2601851835201d11e5805250ecffc703d0b0cd6)

worldedit-core/src/main/java/com/sk89q/worldedit/command/util/SuggestionHelper.java

@@ -149,7 +149,8 @@ public final class SuggestionHelper {
         if (input.isEmpty() || input.equals(":")) {
             final Set<String> namespaces = registry.getKnownNamespaces();
             if (namespaces.size() == 1) {
-                return registry.keySet().stream();
+                int def = namespaces.iterator().next().length() + 1; // default namespace length + ':'
+                return registry.keySet().stream().map(s -> s.substring(def));
             } else {
                 return namespaces.stream().map(s -> s + ":");
             }
@@ -164,7 +165,8 @@ public final class SuggestionHelper {
             // don't yet have namespace - search namespaces + default
             final String lowerSearch = input.toLowerCase(Locale.ROOT);
             String defKey = registry.getDefaultNamespace() + ":" + lowerSearch;
-            return Stream.concat(registry.keySet().stream().filter(s -> s.startsWith(defKey)),
+            int defLength = registry.getDefaultNamespace().length() + 1;
+            return Stream.concat(registry.keySet().stream().filter(s -> s.startsWith(defKey)).map(s -> s.substring(defLength)),
                     registry.getKnownNamespaces().stream().filter(n -> n.startsWith(lowerSearch)).map(n -> n + ":"));
         }
         // have a namespace - search that