[DOCS][MINOR] Remove sentence about Mesos not supporting cluster mode.

Docs change to remove the sentence about Mesos not supporting cluster mode.

It was not.

Author: Michael Gummelt <mgummelt@mesosphere.io>

Closes #12249 from mgummelt/fix-mesos-cluster-docs.

docs/submitting-applications.md

@@ -58,8 +58,7 @@ for applications that involve the REPL (e.g. Spark shell).
 
 Alternatively, if your application is submitted from a machine far from the worker machines (e.g.
 locally on your laptop), it is common to use `cluster` mode to minimize network latency between
-the drivers and the executors. Note that `cluster` mode is currently not supported for
-Mesos clusters. Currently only YARN supports cluster mode for Python applications.
+the drivers and the executors. Currently only YARN supports cluster mode for Python applications.
 
 For Python applications, simply pass a `.py` file in the place of `<application-jar>` instead of a JAR,
 and add Python `.zip`, `.egg` or `.py` files to the search path with `--py-files`.