RFR: 8327738: Remove unused internal method sun.n.w.p.h.HttpURLConnection.setDefaultAuthenticator

[Eirik Bjørsnøs]

Please review this cleanup PR which removes the internal, unused method `sun.n.w.p.h.HttpURLConnection.setDefaultAuthenticator` with associated code.

This was discovered while investigating methods annotated with `@Deprecated`, but missing `@deprecated` javadoc tags.

The method sets a private static field which is read in various places. This field and its uses is also removed. 

Testing: No tests changes in this PR, this is purely a cleanup removal of unused code.

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Commit messages:
 - Fix compilation issue
 - Remove HttpURLConnection.setDefaultAuthenticator, the static field defaultAuth and the uses of this field
 - Update copyright year
 - Remove trailing period from @deprecated note

Changes: https://git.openjdk.org/jdk/pull/18178/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18178&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327738
  Stats: 45 lines in 1 file changed: 0 ins; 44 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18178.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18178/head:pull/18178

PR: https://git.openjdk.org/jdk/pull/18178