RFR: 8307808: G1: Remove partial object-count report after gc

[Albert Mingkun Yang]

Simple removing object-count event in the case of incomplete-marking.

Test: hotspot_gc

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Commit messages:
 - g1-remark-obj-count

Changes: https://git.openjdk.org/jdk/pull/13897/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13897&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307808
  Stats: 47 lines in 2 files changed: 17 ins; 30 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13897.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13897/head:pull/13897

PR: https://git.openjdk.org/jdk/pull/13897