RFR: 8223804: [macos] remove obsoleted reference to security framework in launcher code

[Phil Race]

Bug: https://bugs.openjdk.java.net/browse/JDK-8223804
Webrev: http://cr.openjdk.java.net/~prr/8223804/

This is a small cleanup fix.
When doing a previous launcher fix : 
https://bugs.openjdk.java.net/browse/JDK-8222819
I failed to check if the removal there meant there were now unused 
imports in the
affected source file. There was one. And it seems there is also no 
longer a need to link
against the Security framework either.

-phil.