This PR reverts the fix from [JDK-8339166](https://bugs.openjdk.org/browse/JDK-8339166) because it increases the runtime of the test a lot. Instead a full gc is requested via the whitebox api. This solves the issues (see bug description) and it is also clearer and more reliable that allocating objects and classes expecting a gc because of the small heap. The heap setting is also removed since it is not needed anymore.
#### Testing: Duration Running HiddenClassUnloading with fastdebug Builds I'm giving the minimum of a few runs because durations vary by +/- 10s. Linux / x86_64: After JDK-8339166: 3m15s JDK-8339166 reverted: 50s PR: 50s macOS / M1: After JDK-8339166: 2m30s JDK-8339166 reverted: 30s PR: 30s Linux / ppc64le After JDK-8339166: 12m30s JDK-8339166 reverted: 2m30s (failure: no classes unloaded) PR: 2m30s (success) ------------- Commit messages: - Call WhiteBox::fullGC() for class unloading - Revert "8339166: java/lang/String/concat/HiddenClassUnloading.java fails on AIX and Linux ppc64le after JDK-8336856" Changes: https://git.openjdk.org/jdk/pull/23137/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23137&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8347817 Stats: 13 lines in 1 file changed: 10 ins; 0 del; 3 mod Patch: https://git.openjdk.org/jdk/pull/23137.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/23137/head:pull/23137 PR: https://git.openjdk.org/jdk/pull/23137
