8373557: Remove stale comments after JDK-8372584

[mmm-choi]

This is a backport of JDK-8373557 (dc1b0b5f) to 25u.

This is the third of three related backports and must be applied after JDK-8372584 (#621):

1. JDK-8372625 (#620): Removes the now-unnecessary supports_fast_thread_cpu_time dual-path logic. This is the prerequisite.
2. JDK-8372584 (#621): Replaces /proc parsing with clock_gettime. This is the optimization.
3. JDK-8373557 (this PR): Removes comments made stale by JDK-8372584.

It removes comments in os_linux.cpp and os.hpp that became stale/incorrect after JDK-8372584 (for example the "very slow /proc fs" description, which no longer reflects the implementation). Included for parity with mainline so 25u does not carry misleading comments.

Clean backport

This applied cleanly with no conflicts. The change is comment-only.

Testing

Built release on linux-x86_64 and linux-aarch64 (comment-only change). Verified the full 3-commit stack against the thread-CPU-time test set (see the JDK-8372584 PR #621) and all pass.

---

• I confirm that I make this contribution in accordance with the OpenJDK Interim AI Policy.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8373557 needs maintainer approval

Issue

• JDK-8373557: Remove stale comments after JDK-8372584 (Bug - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk25u-dev.git pull/622/head:pull/622
$ git checkout pull/622

Update a local copy of the PR:
$ git checkout pull/622
$ git pull https://git.openjdk.org/jdk25u-dev.git pull/622/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 622

View PR using the GUI difftool:
$ git pr show -t 622

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk25u-dev/pull/622.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back mmm-choi! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[mlbridge]

Webrevs

• 00: Full (077e9f35)