JDK 12 RFR of JDK-8206439: Remove javac -source/-target 6 from langtools regression tests

[joe darcy]

Hello,

Laying some groundwork for the future removal of javac's -source/-target 
6 later in JDK 12, please review this initial pass to remove most usages 
of -source/-target 6/1.6 from the lantools regression tests:

     http://cr.openjdk.java.net/~darcy/8206439.0/

A number of 6-specific foo.out files are removed. Various other *.out 
files are adjusted to accommodate removal of a @compile line containing 
-source or -target 6.

Thanks,

-Joe