8217474: Remove WhiteBox.getConcurrentGCPhases()
Summary: Remove function and supporting infrastructure.
Reviewed-by: shade, tschatzl
^build/
^dist/
^.idea/
nbproject/private/
^webrev
^.src-rev$
^.jib/
\.DS_Store
\.metadata/
\.recommenders/
test/nashorn/script/external
test/nashorn/lib
NashornProfile.txt
.*/JTreport/.*
.*/JTwork/.*
.*/.git/.*