RFR: 8309603: Deallocate hashtables in ClassLoaderData::unload

[Chad Rakoczy]

[JDK-8309603](https://bugs.openjdk.org/browse/JDK-8309603)

Memory is released in `ClassLoaderdata::~ClassLoaderData` for the dictionary and module hashtables but they could be deleted earlier in `ClassLoaderdata::unload`. Since we're unloading the class loader is no longer being used for lookup.

Additional testing:
- [x] Linux x86_64 fastdebug `tier2`
- [x] Linux x86_64 release `tier2`
- [x] Linux x86_64 fastdebug `gtest:all`
- [x] Linux x86_64 release `gtest:all`
- [ ] Linux x86_64 fastdebug `test/hotspot/jtreg/runtime`
- [ ] Linux x86_64 release `test/hotspot/jtreg/runtime`

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Commit messages:
 - 8309603: Deallocate hashtables in ClassLoaderData::unload

Changes: https://git.openjdk.org/jdk/pull/14820/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14820&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309603
  Stats: 28 lines in 1 file changed: 14 ins; 14 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14820.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14820/head:pull/14820

PR: https://git.openjdk.org/jdk/pull/14820