Deprecate the policytool command line tool, and target its removal for JDK 10.

The policytool is a tool with a GUI for editing policy files. However, it is an old tool with a clunky legacy UI and is not widely used - a survey on security-dev on its usage only revealed one user. Most users edit policy files by hand. Hence, we don't think it provides much value and would like to remove it so that we no longer have to support it.

A CCC should be filed and a correspond docs bug should be filed to update the man pages for policytool to contain a prominent note such as the following:

Note: The policytool tool has been deprecated since JDK 9 and is planned to be removed in the next major JDK release.

Optionally, we should consider printing a similar warning whenever policytool is run.