RFR: 8272196: Remove unused class ParStrongRootsScope

[Albert Mingkun Yang]

Trivial change of removing an unused class definition.

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Commit messages:
 - pgc

Changes: https://git.openjdk.java.net/jdk/pull/5064/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5064&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272196
  Stats: 15 lines in 2 files changed: 0 ins; 15 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5064.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5064/head:pull/5064

PR: https://git.openjdk.java.net/jdk/pull/5064