Integrated: renaming NULLCHK2 to NULLRESTRICTEDCHK

[Vicente Romero]

simple constant renaming as suggested by Remi

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Commit messages:
 - renaming NULLCHK2 to NULLRESTRICTEDCHK

Changes: https://git.openjdk.org/valhalla/pull/1865/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1865&range=00
  Stats: 17 lines in 9 files changed: 1 ins; 3 del; 13 mod
  Patch: https://git.openjdk.org/valhalla/pull/1865.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1865/head:pull/1865

PR: https://git.openjdk.org/valhalla/pull/1865