remove conditional checkAllTopLevel feature

This checkAllTopLevel doesn't really make sense as a feature. 

Imagine you are compiling a C program, and part of the C program was broken (e.g., has a type error) but because your main procedure doesn't use that part, the C compiler doesn't check it, and so doesn't show you that part is broken.

That would be unexpected for it to allow you to just leave a part broken, and not inform you. 

Daffodil should use a similar principle when compiling DFDL schemas. 

It should validate all files.

It should do all static checking on all parts of the schema.

This is different from generating a parser/unparser or generating code. That aspect (which is really the runtime/backend) should occur only for the root element, and recursively what is needed for it. Perhaps someday we should allow compilation to be specified for more than one root, so that we can avoid redundant compilation for say, two roots, one is message, and one messages (for testing/parsing just individual messages, or streams of them, in the same compilation unit). 

But for now, one root will suffice. 

This ticket is about eliminating the on/off checkAllTopLevel feature - which turns off checking of the whole schema. That's the part that really doesn't make sense.