Simplify SessionTable with ConcurrentHashMap for thread safety#2

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LipiLee wants to merge 3 commits intoattdevsupport:masterfrom

Commits on Jun 20, 2017

Remove a duplicated INTERNET permission as the build have gotten the below warning
LipiLee
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Simplify SessionTable with ConcurrentHashMap for thread safety
LipiLee
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Commits on Jun 23, 2017

Remove the unnecessary synchronized keywords
LipiLee
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