Remove nullable annotations directives from Scripting

[BCSharp]

Since all files in Microsoft.Scripting are annotated, it enables nullable annotations at the whole project level, rather than individually at the beginning of each file.

Two generated files still have directive #nullable enable because nullability project setting does not apply to generated files. But something has to be done with them:

• one is generated and checked during tests by IronPython — this is inappropiate for the DLR repo to depend on the IronPython repo;
• the other is "self contained" but being generated by IronRuby, clearly now defunct.

Perhaps best would be to use Roslyn code generators.

There are much more such cases in Microsoft.Dynamic.

[slozier]

Perhaps best would be to use Roslyn code generators.

Agreed on this, been wanting to look into those for a while, but never find the time. I don't like the dependency on ironpython.