Remove -print-dbginfo as it is unused & bitrotten.

This pass hasn't been touched in two years & would fail with assertions against
the current debug info metadata format (the only test case for it still uses a
many-versions old debug info metadata format)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176707 91177308-0d34-0410-b5e6-96231b3b80d8