Fix depends_on in Compose file v3 reference (#2278)

* docker swarm does not respect depends_on

Swarmkit does not seem to have the concept of starting services in a particular order.

Tested with docker 1.13.1. Also, `docker-compose bundle` warns us about depends_on being unsupported.

* Remove condition form of depends_on from the V3 compose file docs.

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

compose/compose-file/index.md

@@ -343,38 +343,19 @@ Simple example:
       db:
         image: postgres
 
-> **Note:** `depends_on` will not wait for `db` and `redis` to be "ready" before
+> **Note:** There are several things to be aware of when using `depends_on`:
+>
+> - `depends_on` will not wait for `db` and `redis` to be "ready" before
 >   starting `web` - only until they have been started. If you need to wait
 >   for a service to be ready, see [Controlling startup order](/compose/startup-order.md)
 >   for more on this problem and strategies for solving it.
+>
+> - Version 3 no longer supports the `condition` form of `depends_on`.
+>
+> - The `depends_on` option is ignored when
+>   [deploying a stack in swarm mode](/engine/reference/commandline/stack_deploy.md)
+>   with a version 3 Compose file.
 
-A healthcheck indicates you want a dependency to wait
-for another container to be "healthy" (i.e. its healthcheck advertises a
-successful state) before starting.
-
-Example:
-
-    version: '2.1'
-    services:
-      web:
-        build: .
-        depends_on:
-          db:
-            condition: service_healthy
-          redis:
-            condition: service_started
-      redis:
-        image: redis
-      db:
-        image: redis
-        healthcheck:
-          test: "exit 0"
-
-In the above example, Compose will wait for the `redis` service to be started
-(legacy behavior) and the `db` service to be healthy before starting `web`.
-
-See the [healthcheck section](#healthcheck) for complementary
-information.
 
 ### dns