Small rewording about history server use case

Hello
PR #10991 removed the built-in history view from Spark Standalone, so the history server is no longer useful to Yarn or Mesos only.

Author: Hervé <dud225@users.noreply.github.com>

Closes #17709 from dud225/patch-1.

(cherry picked from commit 34767997)
Signed-off-by: Sean Owen <sowen@cloudera.com>