RFR: 8254576: ZGC: Clean up timers in roots iterators [v2]

[Per Liden]

> Some of the timers in roots iterators are no longer that interesting after JDK-8253180 (concurrent thread stack
> scanning). I propose we remove them. This patch also adjusts the line break of a comment and moves a closure closer to
> the function where it's used.

Per Liden has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains
one commit:

  8254576: ZGC: Clean up timers in roots iterators

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Changes: https://git.openjdk.java.net/jdk/pull/605/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=605&range=01
  Stats: 36 lines in 2 files changed: 6 ins; 26 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/605.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/605/head:pull/605

PR: https://git.openjdk.java.net/jdk/pull/605