Cleanup work in preparation of future development:

1)	Removal of simple delta and eager delta. Tserved their purpose, and I don’t see their value in our next generation generator.
2)	Removal of extensions. Namely Klee, Crest, CoverageTest, Splat. As I understand, they are just different ways to output a randomly generated AST. A future generator should take a template-based approach to customize outputting.
3)	Removal of exhaustive mode (DFS) and output file splitting. The ERROR_GUARD macros are removed as well.
4)	Removal of generation customizations made to Compcert and MSP. I want to shift the burden of customizations to future users of Csmith. We could provide ways to switch on/off generation logic, and it’s up to the users to use a descriptive language (we provide) to turn on/off certain things.