RFR: 8287771: Remove useless G1 After GC summary refinement and sampling thread times [v2]

[tqxia]

> In the "After GC summary" printed by gc+remset=trace and G1RemsetStatsSummaryPeriod > 1 we print refinement and sampling thread times. However during GC neither thread types are active, so it always prints zeros.
> 
> Remove the printing of these unnecessary values in the after gc summary.

tqxia has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8287771: Remove useless G1 After GC summary refinement and sampling thread times

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9106/files
  - new: https://git.openjdk.org/jdk/pull/9106/files/f8d1c1ad..a2c7dde2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=9106&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=9106&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9106.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9106/head:pull/9106

PR: https://git.openjdk.org/jdk/pull/9106