RFR: JDK-8303181: Memory leak in ClassLoaderExt::setup_app_search_path

[Justin King]

Fix memory leak by removing unnecessary `os::strdup` call. The string is passed as a const pointer to all functions.

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Commit messages:
 - Remove unnecessary strdup

Changes: https://git.openjdk.org/jdk/pull/12748/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12748&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303181
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12748.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12748/head:pull/12748

PR: https://git.openjdk.org/jdk/pull/12748