RFR: 8263964: Redundant check in ObjectStartArray::object_starts_in_range

[Albert Mingkun Yang]

Trivial change of removing a redundant check and some general cleanup in the surrounding code.

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Commit messages:
 - array

Changes: https://git.openjdk.java.net/jdk/pull/3117/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3117&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263964
  Stats: 8 lines in 2 files changed: 0 ins; 6 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3117.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3117/head:pull/3117

PR: https://git.openjdk.java.net/jdk/pull/3117