hotfix for reflection tests on Windows

Removes the Unix-specific command-line sanity check put in place in recently
committed reflection tests.

On Windows, something like `C:\Java\jdk1.6.0_24-x64\jre\bin\java` might
be a valid command (pointing to `java.exe` or `java.bat`) even if
the eponymous file does not exist.
Merge pull request #3062 from xeno-by/topic/broken-windows

hotfix for reflection tests on Windows