RFR: 8256392: C2: Various Node cleanups [v2]

[Claes Redestad]

> - Unused methods:
>  Node::walk, walk_, nop, lookup, rpop
>  Node_Array::reset, sort
> - Disallowing 0 as values to OptoNodeListSize and OptoBlockListSize can simplify some logic: e.g., Node_Array::_max > 0 becomes an invariant (with reset unused and removed)

Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:

  Add back Node::lookup: used by ppc

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1223/files
  - new: https://git.openjdk.java.net/jdk/pull/1223/files/4bd17404..c5f54790

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1223&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1223&range=00-01

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1223.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1223/head:pull/1223

PR: https://git.openjdk.java.net/jdk/pull/1223