RFR: 8341168: Cleanup dead code after JDK-8322630 [v2]

[Axel Boldt-Christmas]

> [JDK-8322630](https://bugs.openjdk.org/browse/JDK-8322630) / #17495 removed the the concept of ICStubs, InlineCache buffers and related safepoints.
> 
> There are a handfull of references and auxiliary constructs still in the code, I propose we clean these out.
> 
> This removes the unused:
>  * Experimental `InlineCacheBufferSize` option
>  * `InlineCacheBuffer_lock` mutex
>  * `Thread::_missed_ic_stub_refill_verifier` field
>  * `VM_ICBufferFull` VM operation

Axel Boldt-Christmas has updated the pull request incrementally with one additional commit since the last revision:

  Add newline

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21255/files
  - new: https://git.openjdk.org/jdk/pull/21255/files/3c6758dd..6fb323b2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21255&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21255&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21255.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21255/head:pull/21255

PR: https://git.openjdk.org/jdk/pull/21255