RFR: Update nmethod caching and clean up unused/duplicate methods

[Ashutosh Mehra]

This PR updates nmethod caching to be based on caching of CodeBlob. It also cleans up some dead code and duplicate methods.

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Commit messages:
 - More cleanup
 - Fix compile failures
 - Refactor nmethod caching
 - Replace apply_relocations with fix_relocations

Changes: https://git.openjdk.org/leyden/pull/71/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=71&range=00
  Stats: 685 lines in 7 files changed: 102 ins; 459 del; 124 mod
  Patch: https://git.openjdk.org/leyden/pull/71.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/71/head:pull/71

PR: https://git.openjdk.org/leyden/pull/71