Use standard Java's UncheckedIOException in JRTUtil

[HannesWell]

What it does

Use standard Java's UncheckedIOException in JRTUtil instead of a similar custom class.

Author checklist

• [ ] I have thoroughly tested my changes
• [x] The change is following the coding conventions
• [x] I have signed the Eclipse Contributor Agreement (ECA)

[HannesWell]

@iloveeclipse or @akurtakov can you please review this?