RFR: Update nmethod caching and clean up unused/duplicate methods [v6]

[Ashutosh Mehra]

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

Ashutosh Mehra has updated the pull request incrementally with one additional commit since the last revision:

  Consolidate handling of asm remarks and dbg strings
  
  Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>

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Changes:
  - all: https://git.openjdk.org/leyden/pull/71/files
  - new: https://git.openjdk.org/leyden/pull/71/files/e9cafdee..f57cb1d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=leyden&pr=71&range=05
 - incr: https://webrevs.openjdk.org/?repo=leyden&pr=71&range=04-05

  Stats: 160 lines in 5 files changed: 34 ins; 66 del; 60 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