Fix out of date zipkin exporter docs (open-telemetry#4995)

exporters/zipkin/README.md

@@ -21,37 +21,9 @@ spans will be sent to a Zipkin endpoint running on `localhost`:
 ZipkinSpanExporter exporter =
         ZipkinSpanExporter.builder()
             .setEndpoint("http://localhost/api/v2/spans")
-            .setServiceName("my-service")
             .build();
 ```
 
-Service name and Endpoint can be also configured via environment variables or system properties.
-
-```java
-// Using environment variables
-ZipkinSpanExporter exporter =
-        ZipkinSpanExporter.builder()
-            .readEnvironmentVariables()
-            .build()
-```
-
-```java
-// Using system properties
-ZipkinSpanExporter exporter =
-        ZipkinSpanExporter.builder()
-            .readSystemProperties()
-            .build()
-```
-
-The Zipkin span exporter will look for the following environment variables / system properties:
-* `OTEL_ZIPKIN_SERVICE_NAME` / `otel.zipkin.service.name`
-* `OTEL_ZIPKIN_ENDPOINT` / `otel.zipkin.endpoint`
-
-
-## Compatibility
-
-As with the OpenTelemetry SDK itself, this exporter is compatible with Java 8+ and Android API level 24+.
-
 ## Attribution
 
 The code in this module is based on the [OpenCensus Zipkin exporter][oc-origin] code.