RFR: 8253539: Remove unused JavaThread functions for set_last_Java_fp/pc

[Coleen Phillimore]

These functions are also unused and in the thread_platform.hpp files.  _last_Java_sp and _last_Java_fp are set in the
assembly code for platforms that use these (x86, arm32 and aarch64).  The shared runtime code never sets these, or
should it. last_Java_fp() is always called through JavaFrameAnchor, so that function is not needed.
last_Java_fp_offset() is used and needs to be in these platform dependent files because not all platforms save
last_Java_fp.

Tested with build on arm32 and tier1 on Oracle platforms including aarch64.

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Commit messages:
 - 8253539: Remove unused JavaThread functions for set_last_Java_fp/pc

Changes: https://git.openjdk.java.net/jdk/pull/324/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=324&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253539
  Stats: 35 lines in 9 files changed: 0 ins; 28 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/324.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/324/head:pull/324

PR: https://git.openjdk.java.net/jdk/pull/324