Remove Support/Options.h, it is unused

It was added in 2014 in 732e0aa9 with one use in Scalarizer.cpp.
That one use was then removed when porting to the new pass manager in
2018 in b6f76002.

While the RFC and the desire to get off of static initializers for
cl::opt all still stand, this code is now dead, and I think we should
delete this code until someone is ready to do the migration.

There were many clients of CommandLine.h that were it transitively
through LLVMContext.h, so I cleaned that up in 4c1a1d3c.

Reviewers: beanz

Differential Revision: https://reviews.llvm.org/D70280