RFR: 8253457: Remove unimplemented register stack functions

[Coleen Phillimore]

Please review removed functions left over from Itanium.

Ran tier1 testing on Oracle platforms (linux-x64, macos-x64, windows-x64 and linux-aarch64) and built on
linux-arm32,linux-ppc64le-debug,linux-s390x-debug,linux-x64-zero.

Thanks,
Coleen

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Commit messages:
 - 8253457: Remove unimplemented register stack functions

Changes: https://git.openjdk.java.net/jdk/pull/300/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=300&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253457
  Stats: 179 lines in 12 files changed: 0 ins; 169 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/300.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/300/head:pull/300

PR: https://git.openjdk.java.net/jdk/pull/300