RFR: 8358729: jdk/internal/loader/URLClassPath/ClassnameCharTest.java depends on Applet [v5]

[Justin Lu]

> Please review this PR which finishes Applet removal for the test: jdk/internal/loader/URLClassPath/ClassnameCharTest.java.
> 
> `testclasses.jar` is updated such that the two classes no longer extend Applet.
> 
> 
> $ javap fo\ o.class 
> public class fo o {
> }
> $ javap æ$'\302\211'$'\302\213'å$'\302\206'$'\302\214'.class 
> public class 手册 {
> }
> 
> 
> The bug description of [JDK-8358729](https://bugs.openjdk.org/browse/JDK-8358729) contains the original `javap` output for those classes.
> 
> Additionally, the security APIs that were marked for removal are also removed from this test as well.

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

  Address review - Convert to JUnit, correct comment typo, remove 'Infra' methods

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25703/files
  - new: https://git.openjdk.org/jdk/pull/25703/files/47f62aa2..02c76c74

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25703&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25703&range=03-04

  Stats: 110 lines in 1 file changed: 22 ins; 61 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/25703.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25703/head:pull/25703

PR: https://git.openjdk.org/jdk/pull/25703