RFR: Purge partial heuristics and connection matrix infrastructure

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/remove-partial/webrev.01/

As discussed earlier [1], this patch removes partial heuristics and associated matrix machinery.
This greatly simplifies the codebase.

Testing: x86_64 tier3_gc_shenandoah {fastdebug|release}, aarch64 build

[1] http://mail.openjdk.java.net/pipermail/shenandoah-dev/2018-September/007385.html