Revert Autogenerate the shebang lines for tools/opt-viewer

This reverts r369486 (git commit 8d183848)

The opt-viewer tests don't pass after this change, and fixing them isn't
trivial. opt-viewer.py imports optmap, which requires adjusting
pythonpath, which is more work than I'm willing to do to fix forward.

llvm-svn: 370095