RFR: 8297301: Cleanup unused methods in JavaUtilJarAccess [v7]

[pandaapo]

> The cache named `signerToCodeSource` in `JarVerifier` is never used now.

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

  Modify as reviews.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11072/files
  - new: https://git.openjdk.org/jdk/pull/11072/files/fb933804..1aa65b2b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11072&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11072&range=05-06

  Stats: 10 lines in 1 file changed: 4 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11072.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11072/head:pull/11072

PR: https://git.openjdk.org/jdk/pull/11072