RFR: 8284999: Remove remaining files in src/samples

[Magnus Ihse Bursie]

JEP 298 was about removing demos and samples. Unfortunately, [JDK-8173801](https://bugs.openjdk.java.net/browse/JDK-8173801) which should have removed all files in src/samples, left a few non-source files (key stores and images). These should be removed.

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Commit messages:
 - 8284999: Remove remaining files in src/samples

Changes: https://git.openjdk.java.net/jdk/pull/8294/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8294&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284999
  Stats: 0 lines in 10 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8294.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8294/head:pull/8294

PR: https://git.openjdk.java.net/jdk/pull/8294