RFR: 8231616: Simplify compilation policy hierarchy

[Claes Redestad]

Hi,

after JDK-8231471 there's no need for NonTieredCompPolicy, so I suggest
folding this abstract base class into SimpleCompPolicy. There are also
a few private/protected methods that were virtual before that no longer
needs to be.

Bug:    https://bugs.openjdk.java.net/browse/JDK-8231616
Webrev: http://cr.openjdk.java.net/~redestad/8231616/open.00/

Testing: tier1-3

Thanks!

/Claes