[foreign-memaccess+abi] RFR: Remove PlatformLayout [v3]

[Per Minborg]

> This PR suggests removing the class `PlatformLayout`.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Update copyright years and clean up

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/794/files
  - new: https://git.openjdk.org/panama-foreign/pull/794/files/d9276950..99964974

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=794&range=02
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=794&range=01-02

  Stats: 10 lines in 9 files changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/794.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/794/head:pull/794

PR: https://git.openjdk.org/panama-foreign/pull/794