[flang][test] Remove RUN COMMANDS/EXPECTED OUTPUT/INPUT markers from test/Driver

Uses of these markers are contrary to all other llvm-project subprojects
and carry no information for people who know the basics of a lit test.

I understand that there is an argument "this makes beginners get started
quickly" but I am unsure whether this is strong enough to deviate from
all other projects. https://llvm.org/docs/TestingGuide.html covers the
basics. Actually, some contributors were confused by the markers.

Differential Revision: https://reviews.llvm.org/D128763