RFR: 8283198: Remove src/jdk.hotspot.agent/test

[Francesco Andreuzzi]

According to the README, this is a manual test of `libproc.so`. The test has a non-standard structure, does not compile using the provided `Makefile`, and hasn't run possibly in a long time. Thus, I propose to remove it.

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Commit messages:
 - rm

Changes: https://git.openjdk.org/jdk/pull/27496/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27496&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8283198
  Stats: 408 lines in 6 files changed: 0 ins; 408 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27496.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27496/head:pull/27496

PR: https://git.openjdk.org/jdk/pull/27496