RFR: 8327738: Remove unused internal method sun.n.w.p.h.HttpURLConnection.setDefaultAuthenticator [v2]

[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. A grep for `setDefaultAuthentication` across the JDK repo after this PR returns no matches.

Eirik Bjørsnøs has updated the pull request incrementally with one additional commit since the last revision:

  Delete deprecated interface HttpAuthenticator, which has now fallen out of use

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/18178/files
  - new: https://git.openjdk.org/jdk/pull/18178/files/3f5582ed..87e84827

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18178&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18178&range=00-01

  Stats: 78 lines in 1 file changed: 0 ins; 78 del; 0 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