RFR: 8349564: Clean warnings found in jpackage tests when building them with -Xlint:all [v2]

[Alexey Semenyuk]

> Clean warnings found in jpackage tests when building them with `-Xlint:all` option in Eclipse IDE. 
> 
> They are:
>  - redundant imports (solution: remove)
>  - unused function/fields (solution: remove)
>  - missing SuppressWarnings-s (solution: add what is missing)
>  - redundant SuppressWarnings-s (solution: remove)
>  - raw types used (solution: use wildcard or more specific types if appropriate)
>  - generic varargs (solution: convert to single/double/list arguments)
>  - an incomplete list of enum elements in switch statements (solution: add `default` branch)
> 
> To prevent regression, added `-Xlint:all -Werror` to the compiler command line of all jpackage tests

Alexey Semenyuk has updated the pull request incrementally with one additional commit since the last revision:

  More cleanup

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23455/files
  - new: https://git.openjdk.org/jdk/pull/23455/files/47217bb3..f60c3c59

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23455&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23455&range=00-01

  Stats: 5 lines in 3 files changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23455.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23455/head:pull/23455

PR: https://git.openjdk.org/jdk/pull/23455