8049422: Remove @jdk.Exported

[Alan Bateman]

It's time to remove @jdk.Exported.

As background, this annotation was introduced by JEP 179 in JDK 8 to 
document the supportness of JDK-specific APIs. It will become redundant 
and confusing once we bring the module system into JDK 9. The proposal 
in JEP 261 is to remove it and it seems saner to remove this in jdk9/dev 
in advance rather than trying to carry this in jigsaw/jake.

The webrevs (top, jdk, langtools and nashorn repos) are here:
   http://cr.openjdk.java.net/~alanb/8049422/

The changes are trivial with all usages removed with
    find src -name "*.java" -exec sed -i '/@jdk.Exported/d' {} \;

Skimming the .patch files should be enough to check for any blunders.

The only "real" changes are the hg rm of Exported.java in the jdk repo, 
and the updates to modules.xml and the package list for the javadoc 
build in the top-level repo

Note that jdeps has already been changed to not use this annotation so 
there are no jdeps changes required, only residual comments in one test.

I think I got everything. Joe Darcy created this annotation and knows 
this removal is coming, I'll at least wait for Joe to review before 
pushing this change.

-Alan.