Remove engine test source code

[javabrett]

Since the engine code was removed 8fad7a31784e46486c0fdaac4d387b730d18534b as discussed in #51, the test-source code under test/org/yccheok/jstock/engine should also be removed, to aid with building what remains.

[osascruz]

I agree, I can not compile the src files, a bit useless without the missing parts. Would be nice to have a compiled library so the compilation of the toplevel can works. Thank you !