[lworld] RFR: 8372954: [lworld] Remove old implementation of the substitutability test method

[Paul Hübner]

Hi all,

This change removes the old substitutability test method. The new/alt substitutability test takes the place of the legacy test, and all identifiers with "alt" are removed.

Testing: tiers 1-5 on Linux (x64, AArch64), macOS (x64, AArch64), Windows (x64).

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Commit messages:
 - Years
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into JDK-8372954
 - substitutability contract changed
 - Legacy handling in ProcessHandleImpl
 - typo
 - Test flags
 - Dead stuff
 - Merge branch 'JDK-8372954' of github.com:Arraying/valhalla into JDK-8372954
 - Merge pull request #1 from liach/fix/remove-old-substitutability
 - Nuke old substitutability
 - ... and 1 more: https://git.openjdk.org/valhalla/compare/2ad3ce16...5e3f8d13

Changes: https://git.openjdk.org/valhalla/pull/2012/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2012&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372954
  Stats: 1789 lines in 25 files changed: 4 ins; 1734 del; 51 mod
  Patch: https://git.openjdk.org/valhalla/pull/2012.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2012/head:pull/2012

PR: https://git.openjdk.org/valhalla/pull/2012