[lworld] RFR: 8366239: Remove 'package_to_module' function from imageFile.cpp

[David Beaumont]

Removing the 'package_to_module' function from imageFile.cpp and the associated JNI export.
This code isn't used or referenced from anywhere, and removing it makes adapting the package flags for use with preview mode simpler.

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Commit messages:
 - remove dead code

Changes: https://git.openjdk.org/valhalla/pull/1535/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1535&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366239
  Stats: 139 lines in 4 files changed: 0 ins; 133 del; 6 mod
  Patch: https://git.openjdk.org/valhalla/pull/1535.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1535/head:pull/1535

PR: https://git.openjdk.org/valhalla/pull/1535