RFR: 8275075: Remove unnecessary conversion to String in jdk.hotspot.agent

[Andrey Turbanov]

Cleanup unnecessary toString() calls when conversion will happen implicitly anyway

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Commit messages:
 - [PATCH] Remove unnecessary conversion to String in jdk.hotspot.agent module

Changes: https://git.openjdk.java.net/jdk/pull/5800/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5800&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275075
  Stats: 14 lines in 4 files changed: 0 ins; 1 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5800.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5800/head:pull/5800

PR: https://git.openjdk.java.net/jdk/pull/5800