Delete nonsense

[inducer]

Loopy currently includes a number of things that, when viewed with the benefit of hindsight, don't make a great deal of sense or have outlived their utility. Let's delete them.

• the Fortran "front-end"
• the "single writer heuristic" (to be replaced by as-sequential dependency finding + thinning)
• See also Retire V1 scheduling #1014.
• See also [Enhancement]: Parallelizing a very long kernel is slow #288 as a concrete outcome to be improved.