RFR: 8281268: Resolve duplication of test ClassTransformer class

[KIRIYAMA Takuya]

ClassTransformer.java is duplicated because ClassTransformer.java was copied from test/jdk/com/sun/jdi/lib/jdb to test/lib/jdk/test/lib/util at [JDK-8240908](https://bugs.openjdk.java.net/browse/JDK-8240908). test/lib/jdk/test/lib/util/ClassTransformer.java should be deleted and test/jdk/com/sun/jdi/lib/jdb/ClassTransformer.java should be used. This is because ClassTransformer is used for testing jdi, and it is not appropriate to exist in test/lib/jdk/test/lib/util.
Would you please review this fix?

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

Commit messages:
 - 8281268: Resolve duplication of test ClassTransformer class

Changes: https://git.openjdk.java.net/jdk/pull/8672/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8672&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281268
  Stats: 165 lines in 2 files changed: 0 ins; 163 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8672.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8672/head:pull/8672

PR: https://git.openjdk.java.net/jdk/pull/8672