RFR: 8356783: CompilerTask hot_method is redundant

[Aleksey Shipilev]

This gave me some grief when implementing [JDK-8231269](https://bugs.openjdk.org/browse/JDK-8231269). From the initializations, it looks to me that `CompilerTask::hot_method()` is either `method()` or `nullptr`. In both cases, we do nothing special. So tracking `hot_method` is redundant, and can be purged. This improves performance a little, since it avoids extra handle-izing across compiler code, and of course it simplifies coding as well.

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

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/25185/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25185&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356783
  Stats: 62 lines in 8 files changed: 0 ins; 47 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/25185.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25185/head:pull/25185

PR: https://git.openjdk.org/jdk/pull/25185