RFR (XS): 8222510: Small cleanup for JDK launcher's make file

[Man Cao]

Hi,

Can I have reviews for this small cleanup? It basically removes some dead
and redundant variables and updates comment.
Webrev: https://cr.openjdk.java.net/~manc/8222510/webrev.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8222510

I found these issues while working on the tsan project (
http://hg.openjdk.java.net/tsan/dev/). Some relevant changes previously
touched the code include JDK-8210931, JDK-8199639, JDK-8141444.

And do I need only one review for this change? It seems many build files
changes only have one reviewer.

-Man