RFR: 8354542: Clean up x86 stubs after 32-bit x86 removal

[Aleksey Shipilev]

This cleanup target various x86-specific stubs and related generators. 

Additional testing: 
 - [x] Linux x86_64 server fastdebug, `all`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/24633/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24633&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354542
  Stats: 176 lines in 6 files changed: 0 ins; 67 del; 109 mod
  Patch: https://git.openjdk.org/jdk/pull/24633.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24633/head:pull/24633

PR: https://git.openjdk.org/jdk/pull/24633