Clean doc of previous namespace (#125)

docs/en/setup/service-agent/java-agent/Namespace.md

@@ -1,24 +0,0 @@
-# Namespace
-
-## Background
-SkyWalking is a monitoring tool, which collects metrics from a distributed system. In the real world, a very large distributed system
-includes hundreds of services, thousands of service instances. In that case, most likely, more than one group, 
-even more than one company are maintaining and monitoring the distributed system. Each one of them takes charge of different parts,
-don't want or shouldn't share there metrics.
-
-Namespace is the proposal from this.It is used for tracing and monitoring isolation.
-
-## Set the namespace
-### Set agent.namespace in agent config
-```properties
-# The agent namespace
-# agent.namespace=default-namespace
-``` 
-
-The default value of `agent.namespace` is empty. 
-
-**Influence**
-The default header key of SkyWalking is `sw8`, more in this Cross Process Propagation Headers Protocol.
-After `agent.namespace` is set, the key changes to `namespace-sw8`.
-
-The across process propagation chain breaks, when the two sides are using different namespace.

docs/en/setup/service-agent/java-agent/advanced-features.md

@@ -2,7 +2,6 @@
 
 * Set the settings through system properties for config file override. Read [setting override](Setting-override.md).
 * Use gRPC TLS to link backend. See [open TLS](TLS.md)
-* Monitor a big cluster by different SkyWalking services. Use [Namespace](Namespace.md) to isolate the context propagation.
 * Set client [token](Token-auth.md) if backend open the token authentication.
 * Application Toolkit, are a collection of libraries, provided by SkyWalking APM. Using them, you have a bridge between your application and SkyWalking APM agent.
     * If you want your codes to interact with SkyWalking agent, including `getting trace id`, `setting tags`, `propagating custom data` etc.. Try [SkyWalking manual APIs](Application-toolkit-trace.md).

docs/menu.yml

@@ -32,8 +32,6 @@ catalog:
         path: "/en/setup/service-agent/java-agent/setting-override"
       - name: "Transport Layer Security (TLS)"
         path: "/en/setup/service-agent/java-agent/tls"
-      - name: "Namespace Isolation"
-        path: "/en/setup/service-agent/java-agent/namespace"
       - name: "Token Authentication"
         path: "/en/setup/service-agent/java-agent/token-auth"
       - name: "Manual APIs"