Remove unused local transport constant

Local transport was removed previously but a stale constant was left
behind. This commit removes this unused constant.

core/src/main/java/org/elasticsearch/common/network/NetworkModule.java

@@ -63,7 +63,6 @@ public final class NetworkModule {
 
     public static final String TRANSPORT_TYPE_KEY = "transport.type";
     public static final String HTTP_TYPE_KEY = "http.type";
-    public static final String LOCAL_TRANSPORT = "local";
     public static final String HTTP_TYPE_DEFAULT_KEY = "http.type.default";
     public static final String TRANSPORT_TYPE_DEFAULT_KEY = "transport.type.default";