Without this instruction, the system continues to use the default OpenJDK.  This is confusing since we instruct the practitioner to install Oracle's JDK.

- Ensure only installation instructions are in INSTALLATION.md and only
  instructions for running tests are in TESTS.md.
- Remove install instructions for IDEs:
  - IDEs start to pay dividends when your codebase gets large enough that the refactoring and code navigation features start to seriously increase your efficiency; Exercism programs are, by design, toy-sized;
  - There are far fewer instructions to getting started when doing it from the command-line (and therefore less likely to get wrong).
- Focus on using package managers:
  - these tools provide the right kind of "magic" — you really don't need to know the installation details to start programming;
  - they automatically perform steps that can be hard to describe and do right (less likely to get wrong).