After [JDK-8245241](https://bugs.openjdk.org/browse/JDK-8245241), the field `sun.util.locale.provider.LocaleProviderAdapter#defaultLocaleProviderAdapter` is only written in `<clinit>` and then is not used after. We can remove it.
------------- Commit messages: - 8312521: Unused field LocaleProviderAdapter#defaultLocaleProviderAdapter could be removed Changes: https://git.openjdk.org/jdk/pull/15388/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15388&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8312521 Stats: 11 lines in 1 file changed: 0 ins; 8 del; 3 mod Patch: https://git.openjdk.org/jdk/pull/15388.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/15388/head:pull/15388 PR: https://git.openjdk.org/jdk/pull/15388
