doc/interop: Simplify language to fix missed x-user-ip

doc/interop-test-descriptions.md

@@ -81,9 +81,8 @@ Procedure:
     Client marks the request as cacheable by setting the cacheable flag in the
     request context. Longer term this should be driven by the method option
     specified in the proto file itself.
- 2. Client calls CacheableUnaryCall with `SimpleRequest` request again
+ 2. Client calls CacheableUnaryCall again immediately with the same request and
-    immediately with the same payload as the previous request. Cacheable flag is
+    configuration as the previous call.
-    also set for this request's context.
 
 Client asserts:
 * Both calls were successful